Rough idle - checked IQ - What do you suggest

db252

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2012 Golf 2005 Jetta 2003 Jetta 2001 Golf
Rough idle - checked IQ - What do you suggest (Updated)

The details:
ALH 2001 Golf with 140,000 miles and an auto transmission.
Timing belt, fuel filter, glow plugs, and harness were all replaced along with air filter approx 10,000 miles ago.
No CEL or stored codes.
MAF is good.
Starts great every time.
When driving the car it runs perfect even when stopped and idling.
It's when you put it in park or neutral that it begins to idle rough.
I hooked up to vcds to check timing and IQ. Timing is spot on. The IQ while idling in park or neutral is all over the board from zero to 3.x and everywhere in between which is most likely the cause of the rough idle. Now put the car into drive or reverse and the IQ goes to 3.5 and stays there with no rough idle.
WHY??
Tried searching all over and have some basic areas to start looking but hoping for more insight from the members. Haven't found anyone with same symptoms of being in gear or not with the same results. Everything I can think of points to the IP but again, why would it work perfectly while in drive or reverse?
What say you?
 
Last edited:

Wonderboy

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Mar 10, 2011
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United States
TDI
2002 VW Jetta TDI
When it is hooked up what are the high and low numbers it is registering? Is it a tight group or +/- 10? When my timing was bouncing all over my IP went and I had to learn the hard way stranded on the highway at 5 a.m.
 

gquenstedt

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San Antonio, TX
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'06, '03 x 2, '00
When it is in gear, there is a load on the engine so it needs more fuel to maintain a smooth idle. When in park or neutral there is less load so it needs less fuel, but the IQ has gotten so low that it can't smoothly control it. Search for "hammer mod" and use that to adjust the IQ to at least 3-4. You may also want to consider some new nozzles.
 

vwdieseling

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Lima Ohio
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Beetle, more bugs
I had the same problem does it idle smooth when cold? Mine was contamination in the sending unit. When first started cold it would idle fine until the engine started to warm up. I could hear the fuel pump relay click and and kick out the cold start injector. thats when the idle would goe erratic. I replaced injectors still didn't help. I replaced pump QA with new seals for the sake of it. I was ready to replace the pump when I did some research on white smoke. It was emitting a little from tail pipe on start up until warm. Reason possible fuel restriction causing a lean condition to IP. I Diesel Purged the pump still no result, but better. I removed and replaced my sending unit. There was dirt and fibers at the bottom of the tank. When I bought the car there wasn't a fuel cap so I am assuming thats how the contamination got in the tank. It still idled rough. I then put a full can of Diesel Purge in the tank. I increased the IQ to 6 and drove it about 10 miles. I reset the IQ to 3 and problem solved. I tried Diesel Klean, but would only stablize idle until the tank was empty. Diesel Purge was the only thing that worked. I think that some how what ever was in the tank got through the water seperator filter. Other than that it would be your quantity cam on the pump going out. I believe that whatever stuff that was in the tank contaminated the pump, because when I replaced th QA and seals there was little black pieces of somthing in the fuel that was in the pump that had gotton through the filter. Two or three cans of Diesel Purge is cheaper than buying a pump from the start. I will be contradicted of course. If you really try my solution Diesel Purge will only work Diesel Klean will boost the cetane and mask the problem. There is a post on how to purge, put a full can in your tank as well. It will clean your nozzles as well. You have .157 nozzles and they are expensive the .184's manuels are cheaper. With the number of miles you stated your nozzles are probably good just need purged with pump and tank. The TDI has a scroll fuel system this means fuel is literally sucked by the pump from the tank and injected in the injectors by the IP any blockage or contamination will effect the idle due to the pump quantity cam not getting enough fuel to do its job. This is the rod and round plate that is inside the pump that must be actuated forward before changing the head seal on the pump or it will fall out of place inside the pump housing. I will be contradicted on this by other members, but I have some diesel training on Catapillar diesel engines via the Marine Corp. Unlike the German TDI IP the Catapiller IP can be adjusted for internal componant wear.
 

whitedog

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Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
My Army, College and industry diesel training says that a scroll fuel system has to do with the shape of the scroll on the plungers.

It's what is commonly used in inline pumps. Like a 3406.

Also, that relay for the cold start injector... The N109 is a grounded solenoid, meaning that it has constant power with the ECU providing a variable ground. Most likely the relay that you heard was the glow plug relay.

So there is your contradiction. :D

To the OP: Adjust the IQ.
 

db252

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Location
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2012 Golf 2005 Jetta 2003 Jetta 2001 Golf
Thanks everyone. Great info so far and I'm always up for the cheaper solutions first.

I am a little unsure about doing the hammer mod (I know how to) only because the IQ is perfect when at idle in gear. If I adjust the IQ for idle while in park/neutral either by vcds or hammer mod, won't that change my IQ that is perfect and stable while in gear? I don't want to mess that up since the car runs so good while driving.

To answer questions above,

Wonderboy - My engine timing is perfect. My warm engine IQ at idle in park/neutral is bouncing all over the scale any decimal between 4.0 and 0. It doesn't stay on any number for any period of time. Now in gear, it's a steady 3.5 and purrs like a diesel kitten.

vwdieseling - Yes I have a better idle when it's cold. I think our symptoms sound 100% alike. I will fill the entire tank with diesel purge (not really) but I will definitely give it it's fair share. I am also going to inspect the pressure regulating valve inside the pump. I'm pretty open to getting new injectors just for maintenance reasons however they were tested along with compression and all tests were good.

Please keep the helpful suggestions coming and thanks again everyone.
 

whitedog

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Bend, Oregon
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2004 Jetta that I fill by myself
The specification for IQ is valid at idle, in neutral, so that is the important setting.
 

db252

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2012 Golf 2005 Jetta 2003 Jetta 2001 Golf
I get that but if the reading is bouncing all over the place how can I set it so that it will stay stable? I have no base line to deal with. I know that 3.0 to 5.0 is a normal range for setting but the reading I get is so irregular and all over the spectrum from 0.0 to 4.x.
 

whitedog

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Bend, Oregon
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2004 Jetta that I fill by myself
Tap it and see if it smooths out. I'm just guessing here, but maybe it's so far off that it drops down and the ECU sees the engine starting to stall, so it gives it more fuel to speed up, then it drops back and starts to stall.

Like I said, I'm just guessing.
 

db252

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Ok. I will update with results of the attempted.
 

vwdieseling

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Beetle, more bugs
There is a n109 solenoid that is located in the housing of the pump. This is the acuator solenoid and is located in the front of the pump/ ie cold start injector. This can only be removed with pump out. If this was bad you would see 225 on the far right of the TDI vcds IP timing checker on the bottom scale, these go bad. The relay I was referring to is the one under the dash that is pain in the $%^% to get to. The big black injection pump relay. A reman pump runs $1000.00. I had the same symptoms as you engine cold would idle fine once fuel temp got up to 65C erratic idle. When I was in drive or reverse IQ would stabilize to 3.5 mg. I added the Diesel Purge and set the IQ high to suck the dirt out of the lines and reset to lowest point this is when the idle became stable. An IQ of 6mg is very high and you will have erratic idle that will sound very stressfull on the engine, until you reset to lowest IQ.Thanks by the way, I Knew I would be contradicted. it scared the $%^% out of me too when mine went erratic. Some people stand in the forest and never see the trees. The glowplug relay kicks out after 60 seconds. My erratic idle would start when fuel temp got to about 65 C. This took about three minuets at Ohio ambiant temps for the problem to start. Well over glowplug cycle. (Try it see if it works.) If not replace pump and injectors, I replaced my injectors, but I probably didn't need to. The pump is lubricated by the fuel and you are right to be scared because when fuel is restricted to the pump failure occurs in the pumps internal parts due to lack of lubrication. Good luck have a safe day.
 

whitedog

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2004 Jetta that I fill by myself
Is there a difference between "Contradicted" and "Corrected"?

I still don't understand which relay you are speaking of. Most of the components in the IP get power from the relay 109 (J317) and if that one opens the engine shuts down so I don't think that is the one that you heard. How about the coolant glow plug relay? That one can open and not kill the engine, but it shouldn't make the engine run rough.
 

vwdieseling

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I have on my 2000 Beetle 1.9 ALH what is termed a injection pump relay. Relay number 3AO927181 its a 12V relay. I tried to insert an image, but still have not got the hang of this site yet. It is under the dash on drivers side in relay panel. In a Beetle it is located towards the driver's door high on the relay panel. If you pull this relay you will loose power to the pump. I have the updated 109 relay in my diesel. I collect Volkswagens, I have gassers as well. I stock relays though in most cases I don't need them. All pump functions requiring solenoid actuation are controlled on this relay. The 109 updated grey relay controls all electrical functions/ ie Power Supply. The pump relay is a 9 prong relay.
 

vwdieseling

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On those Cat systems you are correct in line. I am not a detail freak so in some cases I don't explain things completely.
 

vwdieseling

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I was wrong on the relay whitedog the 9 prong is for the O1M transmission, but pull this the pump quits. Its the park reverse relay for the O1M automatic. Thats what I heard. I never stay in the same learning curve, so I am always in the learning mode.
 

whitedog

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I don't know what to say. I have a drawing of all of the stuff to the injection pump. Here is a link.

 

vwdieseling

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Beetle, more bugs
Checked out your schematic easy enough to read. I am learning how to use this site. I am replacing my front struts. This Beetle I bought was ran into the ground by previous owners. I have replaced axles on it and driver side ball joint. The struts are shot all way around. I got quick struts for front two for $158.00 was quoted a price of $1600.00 at local shop to do the fronts. I said I would think about it. I do all my work myself, but I like a brake once in awhile.
 

db252

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2012 Golf 2005 Jetta 2003 Jetta 2001 Golf
Ok. I don't really get it cause I'm pretty sure I did this already without the same result. I rehooked up vcds to check on a few other things on the car and decided to go back and mess with the IQ settings again. It was currently doing everything I expressed before. Lowered the adaption value by 100 and walaa, the IQ locked in at a maximum of 2.4 and was steady. I couldn't believe it and thought this won't last. Drove it around here and there for the day and was just waiting for that erratic idle to return in park or neutral but it never did. Soooo, fixed I guess. I am still going to do some fuel treatments but this case is closed. On to the next.....new post so I'll be looking for advice there to. Thanks for the help and suggestions.
 

vwdieseling

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I had the same symptoms as you did. I have noticed some drift in mine. After our posts, I checked mine. I am worried about pump failure. I have heard that if the IQ is set by vcds that it will drift. My IQ is currently at 3 mg/ but was lower. In some cases when there is pump failure the ecu will increase IQ to compensate. I replaced my sending unit as well due to my fuel situation. I will keep posting on my IP situation because it sounds like we are sharing the same problem. By the way my IQ was off the wall too, until I reset it lower, this is when my idle stabilized as well.
 

db252

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I am having a perfect and stable result still. It's staying right at 2.4 in idle at normal operating temp. Even though the baseline setting is supposed to be between 3.0 and 5.0 I'm happy cause it is as smooth as can be. I maxed out on lowering the adaption value through vcds and from those results don't see the need to do the hammer mod just to get in that range. Hopefully your attempts get your idle stable and that an IP is not in your future.
 

mk3

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03 Jetta GLS 5-speed
Are your nozzles and pump OEM? or modified?

Have you checked the injector balance? I don't know off the top of my head to check this but when you do this in VAG you get a reading for each of the 4 injectors at idle and they are supposed to be within +/2 but normally they are much better than that. I think mine are within .5
 

vwdieseling

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I agree I replaced my injectors on GP. I would Diesel Purge the pump and tank. Mine was due to bad fuel and when I purchased my car it didn't have a fuel cap. The sending unit and tank had dirt in the bottom of them. So far my IQ has drifted .5 is at three still idleing fine. I an restoring mine so the added posts were in reference to some other issues. Hammer mod requires that special socket for the IP cover.
 
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