1z acts up below 1800rpm

Hello everybody! New to the TDI game, but not new to VW at all. I snagged a beautiful 1 owner B4 sedan from a co-worker a few months ago and it has one hiccup. When I'm cruising in any gear below 1800 rpm it acts like it has a misfire if I give it slight throttle, but it clears up sooner the more throttle I give. It rides well otherwise above 1800. The injection pump was leaking and I rebuilt it and set my IQ properly (steady 4.0-4.2), and it was doing this before I touched anything. Idles fine, but every once in a while it'll idle rough for a couple seconds and clear up. Any idea what I should be looking for?
Also, anyone do business with hansautoparts.com? They have some pretty good prices on parts.

Almost1 said:

Hello everybody! New to the TDI game, but not new to VW at all. I snagged a beautiful 1 owner B4 sedan from a co-worker a few months ago and it has one hiccup. When I'm cruising in any gear below 1800 rpm it acts like it has a misfire if I give it slight throttle, but it clears up sooner the more throttle I give. It rides well otherwise above 1800. The injection pump was leaking and I rebuilt it and set my IQ properly (steady 4.0-4.2), and it was doing this before I touched anything. Idles fine, but every once in a while it'll idle rough for a couple seconds and clear up. Any idea what I should be looking for?

Also, anyone do business with hansautoparts.com? They have some pretty good prices on parts.

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Never buy anything from Hans auto parts. That's the infamous "prothe" or Rothenberger enterprises. They have ruined more TDI's than anybody else combined, I'm sure. Do a forum search for them, and you will read story after story of problems with them.

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avoid his scamming behind like an aids d!ck

changed the fuel filter? might have some water in there!

whats the timming graph say?
have you tried running a closed loop of molly diesel purge?

Fuel filter, TB, and vacuum lines including ecu map line were all replaced. I haven't logged timing and have never heard of diesel purge. I'll get back with findings

Almost1 said:

Fuel filter, TB, and vacuum lines including ecu map line were all replaced. I haven't logged timing and have never heard of diesel purge. I'll get back with findings

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Where did you get the parts from? And who rebuilt the injector pump?

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Parts from dieselgeek and I rebuilt it myself

Almost1 said:

Fuel filter, TB, and vacuum lines including ecu map line were all replaced. I haven't logged timing and have never heard of diesel purge. I'll get back with findings

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Glad you are happy with the car. Good car to find and hard to find in decent shape now.

I would check and verify that the fuel stream to the IP is clear of any air. If you see a fairly steady stream of bubbles then it might be due to a leak somewhere. This can cause irregular idle if the air leak is large enough.

Steve

Almost1 said:

Parts from dieselgeek and I rebuilt it myself

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That's good. I'd verify start of injection timing, I haven't done that on the ahu/1z yet, so am unsure on of its the same process as the alh, then check for fuel leakage. How many miles does the car have?

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Mozambiquer said:

That's good. I'd verify start of injection timing, I haven't done that on the ahu/1z yet, so am unsure on of its the same process as the alh, then check for fuel leakage. How many miles does the car have?

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215k and as soon as I get a chance I'm going to log timing. Fuel flow is steady with no bubbles after I purged it from the rebuild.

Update:

Something told me today when I left work to test if my MAF was bad because I remember reading if you unplug it and you get more power, then it's bad. Well I unplugged it and the issue in my original post is 95% fixed. The power delivery is much smoother over the rev range too. I'm still going to log timing to know where I stand, but I think the MAF did have a lot to do with it. The PO did put one of those k&n rip-offs in there

Almost1 said:

The PO did put one of those k&n rip-offs in there

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yea, thats a maf killer and engine trasher right there. throw that POS in the garbage and put the oem style filter back in, Mann is best IMO but any paper filter will do
have you checked out the cold air intake sticky ?
it will be worth taking the intake boot off the intake of the turbo and checking the fins for damage as these filters will trash a turbo given enough time

Almost1 said:

Update:

Something told me today when I left work to test if my MAF was bad because I remember reading if you unplug it and you get more power, then it's bad. Well I unplugged it and the issue in my original post is 95% fixed. The power delivery is much smoother over the rev range too. I'm still going to log timing to know where I stand, but I think the MAF did have a lot to do with it. The PO did put one of those k&n rip-offs in there

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The VW TDI maf doesn't like most aftermarket air filters. I had a 2000 Jetta with the alh that lost power after the previous owner put one of those filters on. Something about the way it flows, it doesn't read right.

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Mozambiquer said:

The VW TDI maf doesn't like most aftermarket air filters. I had a 2000 Jetta with the alh that lost power after the previous owner put one of those filters on. Something about the way it flows, it doesn't read right.

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No it's about that the filter isn't filtering anything other than big debris, it relies on oil to trap the dust, and it will slam the maf with this oil and dust, this kills hot wire mats and clogs this cold ones.

I can't remember, is there a MAF from another generation that works with the B4's?

Almost1 said:

I can't remember, is there a MAF from another generation that works with the B4's?

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MAF from 1996-97 B4 or from 1997-99 Mk3 is Pierburg and will work, anything 99.5 and up (Mk4) will not work and is typically Bosch.

Technically the MAF from a 1998 B5 tdi would work too but since there were only four of those cars brought into the US the probability of finding one is next to zero.

Steve

I'm just now getting back to this after having my car in the shop getting a new exhaust fitted. I put on a brand new MAF and the problem is back. I tested the new MAF by warming the car up and measuring WOT in 4th and it reads a steady ~850mg/str. I will say that at idle the requested air flow is 250mg/srt and the actual never dips below ~420mg/str.

I also measured injection timing and my pump falls dead nut in the middle of the blue line teetering just below. I'm now leaning towards my injectors being worn out

Almost1 said:

Hello everybody! New to the TDI game, but not new to VW at all. I snagged a beautiful 1 owner B4 sedan from a co-worker a few months ago and it has one hiccup. When I'm cruising in any gear below 1800 rpm it acts like it has a misfire if I give it slight throttle, but it clears up sooner the more throttle I give. It rides well otherwise above 1800. The injection pump was leaking and I rebuilt it and set my IQ properly (steady 4.0-4.2), and it was doing this before I touched anything. Idles fine, but every once in a while it'll idle rough for a couple seconds and clear up. Any idea what I should be looking for?
Also, anyone do business with hansautoparts.com? They have some pretty good prices on parts.

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My B4 has been doing this for 15 years.

bigtom111 said:

My B4 has been doing this for 15 years.

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Certainly could be injectors but I have a set of balanced and pop tested bodies with fresh nozzles and my car will still "stumble" or "hickup" but only when im around 1100rpm decelerating while still maintaining light throttle like in traffic. By 1800rpm there is no issues and its smooth as can be. I believe this behavior is a known problem with the stock 1z ecu and can generally be "fixed" with a tune. If its bucking or stumbling at 1800rpm it seems that is abnormal.

4.0 to 4.2 might not be the happy spot. try putting it down to 3.4 and see if it gets beter, try it at 2.4-2.8 and also try it up at 5. worth a shot

have you tried running some liquid molly injector cleaner in a closed loop till its gone? i had a similar issue and it cleared it up but it was up higher

Mongler98 said:

have you tried running some liquid molly injector cleaner in a closed loop till its gone? i had a similar issue and it cleared it up but it was up higher

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What do you mean by running it in a closed loop? I have some I planned on adding to the next tank of fuel.

I think it's overfueling. Is the car tuned? You can usually tell by looking at the Engine module in VCDS: Tuners will leave a label in the upper right hand info block.

Tuned early cars tend to shudder at 1600-1800 RPM if they're overfueling, Tune, or tune plus larger injectors can cause this. I think disconnecting the MAF helped because it cut fueling. MAFs are a rare failure item on these cars.

Try bumping the IQ up higher and see if it helps. And if the car's tuned you may want to get some stock chips and see if that works. Also, I found these cars can shudder if the intake or cylinder head is clogged with carbon. I had a '97 Jetta (same engine) that shuddered with a tune no matter what I did. The previous owner was very elderly and never got the car above 1,500 RPM. Bad enough that the CAT was plugged. And even after replacing that and cleaning the intake it would shudder. I finally gave up on running a tune.

Almost1 said:

What do you mean by running it in a closed loop? I have some I planned on adding to the next tank of fuel.

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Putting it in the tank will make it pretty much useless. The entire point of diesel purge is to run it closed loop.

Closed loop means that you take off the inlet and return fuel lines off the fuel filter and run them into a container full of liqui moy diesel purge. Most people buy little barbed connectors to join 2 hoses and they buy some extra length of hose the same inside diameter as stock to be able to make the stock fuel lines longer. You then put them both into a container (you can even use the bottle of diesel purge although its better if its see through) and start / run the car off ONLY diesel purge. You let the car idle running on the diesel purge and you rev it up some and hold the engine at a few different rpms for a minute or two.

tl;dr diesel purge needs to be run straight not in the tank, look up a video of people running diesel purge and replicate that. I used a mason jar and didn't add extra hose to the fuel lines just shoved them in the mason jar with diesel purge and run the car till its done, then re attach the fuel lines to the filter.

Giberish33 said:

Putting it in the tank will make it pretty much useless. The entire point of diesel purge is to run it closed loop.

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what you say isnt true to any/or much extent. using purge in the tank, a full bottle to a full tank is good maintenance. it works good. to bottle feed (some how mongler comes up with a 'closed loop' term, & you repeated) is a concentrated shot. can do quite a cleaning to pump to injectors.
setting up bottle feed right is the key. i think there is topic w/pics, it may be on this site. (cannt remember off hand which site, use search, or its in DiY, in 101 section). using fuel rated hoses and connectors, (etc), is a better idea, instead of hackey rig-up in post pics.
entire point of purge isnt just one type of usage, like this 'closed loop' term. bottle feeding is one usage, using a full bottle to about 3/4 a tank of fuel to a full tank is another usage. both are acceptable. read bottle.

Mongler98 said:

have you tried running some liquid molly injector cleaner in a closed loop till its gone?

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bottle feeding is what your talking about.

iluvmydiesels said:

what you say isnt true to any/or much extent. using purge in the tank, a full bottle to a full tank is good maintenance. it works good. to bottle feed (some how mongler comes up with a 'closed loop' term, & you repeated) is a concentrated shot. can do quite a cleaning to pump to injectors.
setting up bottle feed right is the key. i think there is topic w/pics, it may be on this site. (cannt remember off hand which site, use search, or its in DiY, in 101 section). using fuel rated hoses and connectors, (etc), is a better idea, instead of hackey rig-up in post pics.
entire point of purge isnt just one type of usage, like this 'closed loop' term. bottle feeding is one usage, using a full bottle to about 3/4 a tank of fuel to a full tank is another usage. both are acceptable. read bottle.
bottle feeding is what your talking about.

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It is a closed loop, no one is coming up with any terms, it's feeding and returning to the container of diesel purge. That is a closed loop as opposed to if only the inlet was in the diesel purge, that would be burning some and returning the rest to the tank.

Why would someone use diesel purge in the tank for maintenance when its far more economical to run ps silver or howes for maintenance? The little bottle of diesel purge is far more expensive than an entire gallon of the other stuff. So it should be used straight for its full cleaning "purge". If someone is using diesel purge it is likely because there is a fuel issue that might be fixed or improved by a strong dose of a cleaner in a short period of time, either it will improve or it won't. At that point you have done some troubleshooting steps.

I never said you couldn't use it in the tank I said it would be pretty much useless, which is true. Diesel purge for its intended use has no place being in the tank. If you have the time to run hundreds of miles of fuel through and the money to do it with diesel purge exclusively, go ahead. You can do the same procedure with most other diesel additives, diesel purge just happens to have one of the highest concentrations of solvents.

just take some fuel hose from inside the can almost to the bottom, and some fuel line from the IP fuel return line, and put that also into the same bottle, the bottle it comes in, nestle it securely somewhere with some duck tape, i just jammed it between the radiator's upper hose . run it till its empty but try not to run it dry, dump the rest thats left into he tank.

i dont see why this is complicated. bottle fed or more correctly termed at intravenous although thats not even correct but i have also herd it termed as a Auxiliary Gas Fuel Tank, thats what there called.
Closed loop is still correct.

Worth looking into if it has a tune or not as IBW suggested. I've experienced a couple 1Z/AHUs with tunes that are very aggressive with timing advance have a similar almost misfire feel to it with very light throttle right around that rev range.

Definitely does not have a tune, but I planned on getting one from Malone to also get rid of the CEL from the new downpipe with no temp sensors.

I've also looked at the idle correction (Group 13) and each group has over 2 (or -2) units of correction, but for some reason cylinder 4 is blank. I'm under the impression those values are bad, but I don't know where to start looking. I planned on cleaning the intake and intercooler, and checking the cam and lifters. The cam looked fine from the TB service, but I didn't inspect too closely.

Almost1 said:

Definitely does not have a tune, but I planned on getting one from Malone to also get rid of the CEL from the new downpipe with no temp sensors.

I've also looked at the idle correction (Group 13) and each group has over 2 (or -2) units of correction, but for some reason cylinder 4 is blank. I'm under the impression those values are bad, but I don't know where to start looking. I planned on cleaning the intake and intercooler, and checking the cam and lifters. The cam looked fine from the TB service, but I didn't inspect too closely.

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Yeah, that's not a good look. Could be an engine issue, worn injectors or pump issue.

The missing field 4 data in block 13 is normal for pre-EDC15 ECUs (year 2000 is when those started, if I recall).

You can look at it as cylinders 1, 2 and 4 in display fields 1, 2 and 3, and injector #3, which has the needle lift sensor, is the baseline for the other 3 to adjust to.

Well, just to start going through the process of elimination on issues that could be changing the injection deviation, I did a compression test yesterday and each cylinder read ~325psi. I still need to inspect the cam and lifters, but I did notice something interesting while watching Group 13. Two cylinders will be at 2.99 and the other will be close to normal, but the two that are high will gradually decrease until the get to around .5 then the idle gets rough. The cylinder that was reading normal will shoot up to 2.99 and one of the ones that was reading high will stay low with the other going high as well. This is a cycle that you can watch repeat itself over and over with two cylinders going high and one staying low, but it's never the same one going low twice in a row.