Erratic idle & Engine Behavior HELP PLEASE!!

[Phillipw311]

Okay so I have noticed ever since it got cold outside a few months back my car hasn't been right. It's got a shudder at an idle and won't hold a steady consistent 903 RPM. It's very erratic whether the motor is hot or cold. I need suggestions because it's giving me a hell of a headache. I am the TDI specialist in my shop and the only one that works on them and my own damn car is kicking my ass. Haha I know that's a common problem with manual trans ALHs with the DMF separating. But I have an 01M auto so that's not the case with mine.

Here's the headache part. It's contingent on ambient air temp. That's the factor. I realized when it warmed up a few days back, it had a smooth consistent idle. Next morning it was cooler so I fired it up. Idled poorly. And still idled poorly once the motor came up to 190°F.

I have VCDS and yes I've obviously started with and checked the basics. My IQ is high intentionally because I'm running DLC 764s and I want it lean. So when it's behaving and the values aren't bouncing all over the place, my IQ is set to 5.2-5.6mg/str. Under basic settings my timing is a HAIR retarded. By that I mean bouncing from 38-45.

Here's what I've replaced, done, and looked at over the past few months just throwing parts at it at this point because I don't know where to go with it since it's got me beat.

1.) ALL filters changed
2.) Crank sensor (genuine)
3.) Tried raising and lowering IQ. No luck.
4.) Replaced fuel temp sensor.
5.) Pulled pressure relief valve off pump inspected collar was a hair slid out popped it back in no change.
6.) checked for air in the fuel system. None.

I don't know what's going on but any input would be great because it's kicking my ass. Oh also I've noticed my EGTs seem higher when it's warmer and idles right and it boosts as should, but it feels gutless. Like it doesn't have the power behind it like it normally does. Crazy thing is when it is cold and idling bad, it's got twice the power (what used to be normal power until this began) the only thing that looks off to me on my measuring blocks is group 007. Fuel temp looks way too high to me. That's why I replaced it. Once it reaches 190°F the fuel temp is 38-46°C. I compared to another known good ALH and it matched right with the intake air temp within 3-5°C whereas mine are way off. So I think my thermostat T needs replacement I believe it has debris in it or is essentially simulating a stuck thermostat therefor causing excessively high fuel temps therefor retarding my timing.

*BUT KEEP IN MIND*, again it's ALL contingent on whatever ambient air temp is. Whether the motor is hot or cold makes no difference. That's what's got me stumped. That's why I don't that the Thermostatic T will do the trick. Because it idles rough cold too. It's also smoky when cold. With an IQ of 5.5mg/str it shouldn't be smoky at all at an idle. Again, being an auto it's got the fuel cooler so I think that's a red flag I don't think it should be that hot regardless. And yes I've checked my IAT (MAP) and it's accurate. So I'm at a loss. Somebody give me something it's driving me crazy. Haha thanks you guys.

 

[bmali98]

Is there possibly a fuel restriction? Maybe a collapsed/kinked line or a plugged sending unit inlet. I think the fuel cooler is on the return to tank line. Maybe the injection pump is heating up because it's overworked and isn't flowing heat out of itself. Easy way to know is run the engine up to temp out of a jerry can. Cost of testing is just hose and barbs. Test with and without the thermal t. You can still run through the filter, get barb caps for the t.

You can bypass the t permanently if you want by getting an early mk3 or mk2 fuel filter. I did this on my mk3 to get rid of air bubbles.

 

[Phillipw311]

Exactly man! That's what I was thinking thanks so much for the feedback. I've ironically I ordered a thermostatic T new this evening through a parts company we use it'll be here tomorrow at noon. I'm just going to wing it. It was $6 for a genuine one my cost what do I have to lose at this point you know?? Lol you're correct about the fuel cooler. It's like literally directly under the passenger side floorboard. Another catch. I am running a 10mm manual pump on my automatic trans car that should have the 11mm. (Long ass story....) but that's why I decided to go with the DLC 764s and go with the larger calibrated nozzle. So with that being said if anything my fuel temps should be lower than my buddy's known good stock ALH with an 11mm pump & 01M trans. It's been in the 50s and mid 60s here in Memphis lately and even at operating temp I don't think there should be any excuse to have fuel temps that damn high. Especially since I'm running the smaller pump producing less heat AND have a cooler. Again, I replaced the sensor thinking it was out of whack and to my shock that too didn't cure it. So I'm thinking its a restriction issue. That's the only thing that could make it contingent on ambient air temp due to fuel density.. Makes sense too. If it's colder its thicker therefore harder to move through whatever's restricting it.

Because again, it idles bad full time when its cold. The colder it is the worse it runs whether it's a cold start or been running for hours at 190°F.. But it runs GREAT off of an idle. So would you lean more towards the restriction route, replace thermostatic t, and then see if the in tank pump is full of **** starving it?? Or would you go the IP timing route..? Just your personal opinion how'd you tackle it?? But I know for a fact it's not sucking air through the clear fuel line from filter to pump. Not bubbling at all or losing prime nothing like that.

 

[bmali98]

I would personally do the jerry can method. That eliminates all possible causes of restriction from the fuel system. If you have an outboard boat engine primer bulb this will make it easier to prime the system. Do the t first. If this doesn't solve it, do the jerry can. That's how I would take this on. Having done all you can already with vagcom, I don't think it will offer any resolution for you aside from monitoring temperature to verify the repair.

 

[Phillipw311]

Can anybody by chance send my a DIY link or YouTube link on how to do that step by step..? I believe I understand the procedure but I'd like to have a video or thread with pics to follow and go off of in doubt. Thanks again for the input guys I really do appreciate it.

 

[Zedbra]

Check the fuel and if that isn't it, possibly check cam wear. I had the same symptoms on my BRM and it was the cam/lobes. I'm starting to get some of the same symptoms on my PD.

 

[Phillipw311]

Really?? That's very interesting as far as I know ALHs aren't too bad about cam wear but I didn't know that it could cause erratic random idle. It's so weird and giving me such a headache. I'm at a dead end because it doesn't matter if the motor temp is 30°F or 210°F. Makes no difference. The only time it idles rough is when it's cooler outside. Such a strange issue to have. Most of the time it's engine temp contingent as far as idle issues. And I have a new ECT in it. It's not but like 6-8 months old and it's accurate. I don't remember if I mentioned that or not. But nonetheless I'm stumped. I'm going to try the thermostatic T this afternoon but I don't think it'll fix it quite honestly but who knows. I'll keep you guys updated and what the verdict is post thermostatic t replacement regardless.

 

[bmali98]

Can anybody by chance send my a DIY link or YouTube link on how to do that step by step..? I believe I understand the procedure but I'd like to have a video or thread with pics to follow and go off of in doubt. Thanks again for the input guys I really do appreciate it.

It would only take removing the 2 lines at the filter from the tank and instead running 2 lines off the filter to a jerry can. Put the primer bulb on the line that goes to the steel barb on the filter. Give the primer a few pumps and fire it up and monitor fuel temp. If you don't prime the fuel system it will stall and you will have to bleed your injector lines. There's a tutorial likely for that but probably not for bypassing your fuel tank. Google "alh injector bleed" and likely something will come up.


Alh having a bad cam isn't common at all. Mostly A pd problem.

 

[Phillipw311]

So... Stupid question. I'm a technician and work on euro cars all day. VW & Audi specifically. I'm the TDI specialist at the shop. Only one that understands them and knows how to work on them. So yes I know how to bleed the fuel system. But here's my question. The thermostatic-T. For TEMPORARY purposes, what's to prevent me from pulling the inlet and outlet from the T branch off and looping them directly together with a brass fitting then taking vacuum caps and capping off the Thermostatic-T so diesel won't go all over creation..? Wouldn't that be easier and simulate the same thing? On that note if yes I can do that, would you put tiny hose clamps over the vacuum caps on fuel filter T? I don't know if there'd be enough pressure in the system to shoot vacuum caps off of the fuel filter (blocked off T) I'm not sure about that.

 

[bmali98]

So... Stupid question. I'm a technician and work on euro cars all day. VW & Audi specifically. I'm the TDI specialist at the shop. Only one that understands them and knows how to work on them. So yes I know how to bleed the fuel system. But here's my question. The thermostatic-T. For TEMPORARY purposes, what's to prevent me from pulling the inlet and outlet from the T branch off and looping them directly together with a brass fitting then taking vacuum caps and capping off the Thermostatic-T so diesel won't go all over creation..? Wouldn't that be easier and simulate the same thing? On that note if yes I can do that, would you put tiny hose clamps over the vacuum caps on fuel filter T? I don't know if there'd be enough pressure in the system to shoot vacuum caps off of the fuel filter (blocked off T) I'm not sure about that.

You could do the caps on the t but that wouldn't eliminate restriction elsewhere if it is elsewhere. Could still be sending unit or lines between. You could run an earlier (mk2 earlier mk3) filter and eliminate the t all together if you want. The return line doesn't touch the filter in these. Not sure on filter rating on earlier filters tho if it filters same or worse ( particle size(microns)). The filter should always be under partial vacuum as your car doesn't have a lift pump unless you installed one. Your injection pump sucks the fuel up to it. Zero chance of blowing the caps off.


Just thought too, could be a plugged tank vent line. That would cause a vacuum in your tank after some driving.

 

[BobnOH]

I'd check all the temperature sensors hot and cold, look for goofy readings. There is one for ambient, damned if I know what it does.
A4 TDI engine measuring blocks/groups

 

[Phillipw311]

You could do the caps on the t but that wouldn't eliminate restriction elsewhere if it is elsewhere. Could still be sending unit or lines between. You could run an earlier (mk2 earlier mk3) filter and eliminate the t all together if you want. The return line doesn't touch the filter in these. Not sure on filter rating on earlier filters tho if it filters same or worse ( particle size(microns)). The filter should always be under partial vacuum as your car doesn't have a lift pump unless you installed one. Your injection pump sucks the fuel up to it. Zero chance of blowing the caps off.


Just thought too, could be a plugged tank vent line. That would cause a vacuum in your tank after some driving.

Right right I have no lift pump. And yeah the return system in fact does go back through the filter I know that much simply because think about it. That's the whole point of the stupid ass Thermostatic T with the Mickey Mouse clip on it in the first place. It doesn't allow fuel to flow back to the tank until it reaches a specific temp. Unless something is wrong with it and it's trashed up stuck etc.. I'm gonna wing it for ****s and gigs just to see if my fuel temp drops significantly before installing the new one I already have. Got it today. I do see what you're saying as far as the in tank pump or lines pre filter being kinked or restricted yes and I do agree with that. But I'm gonna wing it. Again, will post results later.

 

[Phillipw311]

Okay I drove it home with the bypass temporary rig whipped out VCDS and my fuel temp was at 105°F once I made it home from work. My IAT was reading 100°F. My ECT showed 204°F. This was after it'd been idling for like 5 minutes in the driveway. Bypassing the thermostatic-T all together on a day where ambient air temp is 70° doesn't that sound high as hell to you guys..? As far as my fuel & IAT?? Keep in mind I'm running the 10mm pump with DLC 764s and have every bit of Kerma's piping upgrades for volumetric efficiency. Still got stock turbo & intercooler however. If yes then that to me says I've got a fuel restriction. Probably the in tank unit. The crazy thing is this. It's got more power when it's idling rough (cold outside) and I manage to push 44 MPG city consistently if anybody can believe that. Or the fact that the ole 01M has taken the abuse and shifts beautifully.

On a side note another possibility I'm unsure of. My start of injection specified vs. actual. At an idle the specified is 0.4° BTDC. My actual however, bounces around intermittently while idling. It'll go from smooth and right on the $ then it may drop to 0.2° BTDC then sometimes it'll bounce up to 0.7° BTDC. Any thoughts with the newly given info??

 

[bmali98]

I don't know what volume the pump should move through itself at idle but if someone knows the actual amount you could collect the volume in a pail/minute and compare also. Also test the temp in the pail and compare to the temp on the scanner.


Maybe the unreliable/elevated fuel temp causing viscosity issues?

 

[Phillipw311]

Yeah that's an excellent thought as well. I would've never thought about that. I assume there will be a 5-10°F differential between pump reading and in a bucket due to ambient air vs. a super hot IP. Haha that's a good idea though.

On that note I don't know if you've read all the way from the beginning, but I suspected the fuel temp sensor was bad, which is highly unlikely, but I did since the value was so high even though it was cold outside. At this time it was 38-50°F here and that sounded way off. So I put a known good one in mine. I've resealed many pumps so I know how to yank em apart. Haha so I pulled the top off swapped it and it was reading the same. So to me that says it's a mechanical issue. But again, brand new fuel filter. Only thing I hadn't replaced under the hood maintenance wise was the thermostatic t. Bought one today. Just to bypass the setup completely I capped off the existing T and looped the two lines together via brass fitting. Same result. It was warmer today (low 70s) so it didn't idle quite as bad but it's still there. Just not as violent. But it doesn't feel like it has the power it should when it's warm outside. It almost feels like I pulled the VNT solenoid vacuum line off. Just that feeling that it pulls but it's not all there 100% as it used to be. I'd guesstimate 25-30% power loss when it's warmer outside, doesn't idle quite as bad, and doesn't run too strong off an idle. Not like it should. But I know it's boosting I've got NewSouth boost gauges and NewSouth EGT gauge with the extended pyrometer and its boosting. Also another thing, again, my EGTs are higher than I think they should be.

But yes I believe you're on the $ with viscosity. I believe it's starving the IP when cold due to in tank pump restriction and once warm not circulating/cooling fuel properly therefore hot ass fuel which means hotter/thinner diesel leading to the ECU retarding timing. Correct me if I'm wrong but that's what I'm starting to believe is going on.

 

[bmali98]

I think we need to second guess the ecm readings also. The more to compare in ecm to actual measurement the better. Temp is doable. If the fuel actually is near ambient temp then it's still the electrical. Could be some inductive current messing things up elsewhere or resistance somewhere etc.

Why did the pump get changed?

 

[Phillipw311]

Well see that's the thing that's also throwing me off. None of my cold static values really make any sense under group 007. By that I mean like cold engine sat over night plug up VCDS before I fire it and start creating heat. So just cold motor. Switch key on engine off. They should all baseline be the same with ambient air temp and they're not. My ECT, which I replaced less than 20K miles ago with a genuine one, will be showing 10-15°F over ambient air temp..? Then the fuel temp sensor and IAT are off which makes no sense to me. It's a dead giveaway if one is way off but they're all off. They should be within 1-3°C of each other max I would think. Especially cold. Without the motor running. They're all within 10-15°F of each other but really the only one that's accurate within a degree or two is the MAP reading (IAT).

Also my car is remapped. So my MAF specified is like 850 at an idle the actual ranges from 450-500. But that still wouldn't create this problem even if the MAF were bad. I tried unplugging it as well just to check it recently. It ran horrible with it unplugged. So that to me said it was right, accurate, and doing its job. Anyways to narrow it down I restored the original ECU map. No luck. All of my values essentially stayed the same and my spec vs. actual is all over it except for the random spikes when it idles erratically all of the values eradicate in conjunction with the idle. So that makes it damn near impossible to trace. The whole problem is I don't see anything out of whack.

Your last question.. To make a long story short before I knew a ton about ALHs and got super into them, customer had hers towed in. Diagnosed it with a bad injection pump. She wanted to sell it and buy a new one as is and then that happened. So I made her an offer to buy it she cut her losses and I bought it. Because it wouldn't have been worth fixing from her shoes since she wanted it gone. I happened to have a spare ALH motor ironically because another TDI was timed improperly which bent every valve in the head by another shop. Guy brought it to us and said put a motor in it I don't care what it costs just fix it. So before they came to get the core I stole the pump off of it. At the time I didn't know the pump size varied from auto to manual and I put a manual pump on it. So to compensate for the small pump I chose the larger DLC 764s oppose to the DLC 1019s.

 

[bmali98]

I have a feeling if you measure the fuel temp it will be near ambient where it's supposed to be. I have a feeling it is an electrical problem now. I checked all my temps last week cold after only 6 hours and all temps were within 2C of one another (air, fuel, coolant, actual ambient). You're temperatures don't spike like 10C up and down do they? Maybe a bad harness connection somewhere? Maybe non dielectric grease used? If you could get your hands on a known good enough for testing you might get different readings.

 

[Phillipw311]

No no. No spikes or erratic fluctuations when running but riddle me this. My values are WAY the hell off hot and cold. I simply don't get it. Even cold the values aren't the same and from a static cold motor every one of those 3 should be 1-2°C within each other. Once the motor is warm the values get bad off. Again I replaced the fuel temp sensor so I don't believe it's inaccurate. Oh also important fact. Ambient air temp was 59°F this morning and it was still 59°F when I got to work.

First thing this morning key on engine off data before starting car. COLD engine:
Group 007:
Fuel temp- 18.9°C
IAT- 15.3°C
ECT- 18°C

Drove to work 30 minute drive so engine was hot. HOT engine values are way off
Group 007:
Fuel temp- 32.4°C
IAT- 20.7°C
ECT- 93.6°C

 

[bmali98]

K so ya, still thinking fuel restriction then.

 

[Phillipw311]

See that's exactly what I was thinking. Also again, for a refresher, I put a brand new Mahle filter on it 3K miles ago. So I know that's not the problem. So here's the million $ question. How the hell am I supposed to check/diagnose the in tank pump since it literally does nothing supply wise..? Haha there's no pressure being produced on it as you all know. None to speak of really. Like maybe 5psi brand new tops. Haha so how do I find out where my restriction is? Check at filter and pump with a vacuum gauge kit I know that much, but I don't know how strong it should flow. At the filter if it's slower obviously the lines are kinked somewhere. But at the inlet/feed directly on the pump I don't know how fast the flow rate should be and how quick it should start flowing. But given the ambient air temp vs. the fuel temp values with a hot and cold motor you're thinking the culprit of my erratic idle is due to high fuel temps and restriction?? Do you think the temp is too high?? I sure as hell do but I'm not 100% sure. But to me that looks way too hot considering it's running the 10mm pump and it's for the fuel cooler.

 

[BobnOH]

Temperatures look fine.
The ALH doesn't use an in-tank pump (or did I miss something). Easiest check for flow is put a vacuum on the return line at IP and draw fuel. You should get a steady stream. If not, track down the restriction. You could try a diesel purge to clean injectors. Check the little fuel return lines on the injectors. Check Group 013 for balance.

 

[JB05]

Isn't there a check valve in the fuel sender that can get plugged up? I've read here that people drill them out.

 

[bmali98]

There isn't a lift pump. Just lines from front to back and a pickup in the tank. You could use a drill pump to pull fuel up and see how much flow you have. It should be relatively unrestricted.

Also In case someone installed a lift pump sending unit, the sending unit wiring would have a 4 terminal connection rather than 2.

 

[Phillipw311]

No it doesn't have a lift pump retrofitted. It's the OEM one. Never been touched. So, my fuel temp looks normal to you..? In that case that to me says that there's no restriction. What the hell is going on with my car somebody please. Lol my injector return lines are all less than a year old and in very good condition. I've already checked time and time again group 001, 007, & 013. In group 13 they all appear to be balanced there's not one that's like a mile off from the other 3 injectors.

So with that being said where do I go from here..? If you all think my fuel temp is normal and not high then that says to me no restriction therefore I'm at a blank. Dead end. But the baseline values should be pretty damn close from fuel temp to IAT. Again, I compared to a known good stock ALH other than the same tune I have with VCDS with the 11mm pump and auto trans and his fuel temp & IAT were literally on point matching values at operating temp. Whereas mine is roughly 20°F off.

Side note. I traditionally run Redline Cetane booster during the winter to help from cold starts and I quit running it thinking maybe that was the culprit. Of course not. That'd make my life way too easy. Lol but I need input because it's driving me nuts. I don't know if I'm wasting my time checking for a mechanical issue such as a restriction in the fuel system or if I should be hunting an electrical issue. I can't decide to be honest.

 

[UhOh]

You've got large nozzles and you're running retarded. I don't think that this is optimal.

As far as "wanting to run lean," WHY? What you WANT is to optimize, and as far as IQ goes you set it where you minimize smoke and shudder.

Lots of talk about your fuel temps. Not idea on that. I know that I had an oddity with wacko temps recently when was doing some timing on the wife's car: I ignored it, as things seem fine; I think that just sometimes VCDS reports some crap when it comes to this. In your case perhaps I it's possible that fuel temps are elevated because of retarded timing, though I really don't have anything to back up this thought: just kind of thinking out loud.

 

[Phillipw311]

You've got large nozzles and you're running retarded. I don't think that this is optimal.

As far as "wanting to run lean," WHY? What you WANT is to optimize, and as far as IQ goes you set it where you minimize smoke and shudder.

Lots of talk about your fuel temps. Not idea on that. I know that I had an oddity with wacko temps recently when was doing some timing on the wife's car: I ignored it, as things seem fine; I think that just sometimes VCDS reports some crap when it comes to this. In your case perhaps I it's possible that fuel temps are elevated because of retarded timing, though I really don't have anything to back up this thought: just kind of thinking out loud.

Okay. I'm running a 10mm pump. So to compensate for the smaller pump I got the 764s over the 1019s to add/compensate for the smaller pump and for if in the future I decide to upgrade my VNT15, the 764s are more ideal for more boost over the 1019s. I want it on the lean side because that means complete burn and atomization. Guess what? I can drop it to 3.0mg/str and gain 10-15% more power but it hazes at 2,400 RPM and is literally black smoke solid clouds of soot by 3,000 RPM. Complete waste of fuel. And my MPGs go way down when the IQ is low. I've got it leaned out to the point that it doesn't start to haze until 3,400 RPM give or take. So it's atomizing the majority of the fuel throughout the power band. That's why I want it lean. 764s flow like 87% I wanna say over factory. And they atomize a hell of a lot better than OEM nozzles when calibrated properly. So with a factory turbo and fat nozzles I had to dial back the fueling to get optimal power and efficiency without being smoky. I also have an EGR delete and straight pipe off the turbo so no cat. In case you didn't read. Point being it black smokes very easily. So if I drop it to 3.0mg/str it pulls a hair harder out of the hole on a launch but my MPG drops to like 32-36 city depending on my foot. Running at 5.2-5.6 it's a perfect setup. Because it atomizes all of the fuel so none is wasted, I still get the feel and power of large injectors, and I push a consistent 42-44 MPG city with an auto trans and big injectors. Despite my crap idle that's my counterpoint to what you just said.

 

[UhOh]

I'm out of here... (you've brought a lot of the upon yourself by not doing research up front and now you're trying to un-mess the mess you've created- get a tune and get some real expectations)

 

[Phillipw311]

I'm out of here... (you've brought a lot of the upon yourself by not doing research up front and now you're trying to un-mess the mess you've created- get a tune and get some real expectations)

...? Do you even know what you're talking about..? I did plenty of research bud. And "un-mess...?" Are you kidding me right now? It's been modified like this for a long ass time and I haven't ever had troubles till recently and it's only at an idle. I didn't bring any of this upon myself by not researching. Bull ****. I didn't "create a mess" none of this on me it has nothing to do with my modifications. Because I DID MY RESEARCH and I'm a technician that specializes in TDIs so I know what I'm doing don't give me that BS. Secondly, if you had read the entire thing you'd know that I already have had my ECU remapped by Kerma. So don't condecend me and say that it's my fault because I know damn good and well what I've done to it and I did every bit of the work so it was done professionally and I know it's right. And this problem just randomly out of nowhere started occurring I didn't change or alter anything. So there's another counterpoint to your "un-mess the mess I created" bull ****.

 

[Ill Named]

Pull the pick up out of the tank and drill out the check valve. At least eliminate it from the equation.

Then, if that does nothing, open up the wiring loom coming from under the battery and looked for worn through wires. specifically where it attaches to the engine.