2003 a4 jetta blip throttle results in rough idle

[ninedee_golf_tdi]

A fine runnning stock 03 a4 with 01m idles fine upon start. Blip the throttle or drive it then let it idle and the idle spaz's, the iq jumps around and the injector balance maxes out either 1.88 or -1.88. After a few minutes, the idle normalizes until it runs smooth like it should. I put a rebuilt pump on it and another set of injectors neither of which rectified the problem. I don't see any chewed wires, the maf reading looks good as does everything else. What am I missing ? Thanks.

 

[ninedee_golf_tdi]

Guesses are welcomed.

 

[DuraBioPwr]

Maybe getting air in the pump from a rapid vacuum rise on the fuel side (throttle blip). Would take a minute to work the air back out and idle restabilize. Spitballing.

 

[ninedee_golf_tdi]

I considered a fuel issue so I bypassed everything and ran the car off a fuel bottle directly into the pump. No change doing that either. I'm thinking the problem isn't external to the pump.

 

[jmodge]

have you monitored throttle position, timing, boost, and coolant temp while this is happening?

 

[ninedee_golf_tdi]

I graphed the throttle position, seems to increase and decrease smoothly. I did the timing belt and it is correctly set. Coolant temp, air temp and fuel temp are all equal when I start it cold. Havent graphed the boost yet.

 

[BobnOH]

TPS was my first thought. Or a really high IQ value, like 8 or 9.
We see more and more issues with wire/connects as these cars age. Damn hard to find.

 

[Mozambiquer]

Whats the iq at when at idle?

 

[ninedee_golf_tdi]

Cold I'm thinking about 5.0 maybe, then it goes down to 3.6-3.8 when warm.

 

[JDSwan87]

Isn't the IQ like a "slide" inside of the pump? If it is, could the slide be gunked up and/or sticking, causing the issue?

 

[ninedee_golf_tdi]

Sooo.... I'm still putzing with this car. Put a rebuilt pump on it, same stumble. Took the old pump apart, the iq module looked like it was in operating condition, the collar on the shaft slid easily, no rust, no issues to speak of. Put that pump back on and the same stumble still exists. I cut the wiring harness open from under the battery box to the pump 10 pin connector and didn't see any chafes or defects. Any other suggestions ? Thanks.

 

[ninedee_golf_tdi]

This is the only car that does this ? No one else has experienced this ?

 

[JDSwan87]

Do these cars have a fuel temp sensor? If so, after sitting overnight, is your fuel temp close/matching ambient air temp? (My line of thinking is the ECU is reading an abnormally cold fuel temp and adjusting parameters to make it run).

 

[ninedee_golf_tdi]

The fuel temp sensor is a thermistor inside the pump. I checked the three temps a while ago and all seemed close so I ruled that out. When I put the rebuilt pump on it and the stumble was still there, I discounted temps completely. I recently put the old pump back on, stumble still there. Just now with 44 degree ambient temp in the garage, temps are reading fuel 0.0c, air and coolant 10.0c. Maybe the fuel temp sensor is wonky. I'll replace it in a few minutes.

 

[ninedee_golf_tdi]

Bummer, swapped in a new fuel temp sensor, and now the temp readings are 100% equal. but, it still does the same stumbling, bad miss, erratic iq thing. I certainly am scratching my head on this one.

 

[burpod]

crank sensor? try logging 004 while idling and doing the throttle blip. see how the timing tracks?

 

[BobnOH]

Lets assume it's not the pump.
Small air leak somewhere causing fuel (d2+air) mix to be way off. Or a wire/connect somewhere.
Guessing you've tried unplugged MAF, but that is often inconclusive, but might be a clue.

 

[ninedee_golf_tdi]

I ran the engine off of a separate bottle of extreme diesel and d2 to rule out flow restriction, no change. Just swapped the crank position sensor with a junker, no change. MAF and egr look like they're playing nice. I had put a newly rebuilt pump on it, since replaced with the original pump, no change with the rebuilt.

 

[ninedee_golf_tdi]

Still at it. Its easy to duplicate the problem. To summarize what I've done so far:
installed rebuilt pump, since removed, original put back on
swapped crankshaft position sensor
known good ecu swapped
ran engine on separate fuel bottle
maf / egr look normal
disconnected asv, since reconnected
entire harness cut apart from ecu to pump, no defects found
tug tested every wire at the pump, ecu and 3rd injector
throttle pedal graphed and looks linear up and down

Lets assume that this original pump and the rebuilt pump both have a similar gremlin in them that cause the identical rough idle / bouncing iq when the go pedal is blipped, or rpms raised up to 3000rpm +/- and then quickly let back to idle. What would that gremlin be, the iq module, modulating piston, something else ?

Guesses welcome, and thanks Burpod and others for your suggestions.

 

[csstevej]

What about your injectors?
Possible issues going from idle to more power then back to idle.

 

[ninedee_golf_tdi]

This an automatic, the owner had a friend install a used set to try to troubleshoot. The injectors didn't fix the problem, but the used exchange injectors are still installed.

 

[BobnOH]

This may explain why the injector readings jump out of range

Small air leak somewhere causing fuel (d2+air) mix to be way off.

 

[ninedee_golf_tdi]

An internal failure of both pumps is a stretch, but I'm willing to consider that. Just spoke with Kyle at dfis and he wants me to check out the drive plate for wear. If I wanted to disassemble the pump, he gave me other things to check like the cross drive something gadget, but I don't want to disassemble this pump. Both pumps have to have the identical failure for this to happen with both of them.

 

[csstevej]

Yeah that would be very very rare…

 

[ninedee_golf_tdi]

Still scratching my head. After sitting overnight, I started it, blipped the throttle and same results, iq spazzes, idles rough, smokes badly. One thing I noticed is that the timing increases from a value of about 51 (idling smoothly) up to 58-59 after blipping the pedal (and now running roughly) returning to idle and stays there until it normals up. Does the iq affect the timing or does the timing affect the iq ? I started to think the tone ring on the crank might be damaged, but that doesn't make sense since the car drives fine when it wants to. Guesses are always welcome. Thanks.

 

[JDSwan87]

Isn't timing tied to coolant temp?

 

[ninedee_golf_tdi]

And fuel temp and air temp, I think. All three values were 11.7c this morning.

 

[burpod]

stock, timing is set by coolant temp and then advanced for colder air. on the alh, a sharp advance of about 2deg for idle fuel/rpm between 20c and 10c air temps i believe. the timing log looked stable...

 

[DuraBioPwr]

Spitballing again but maybe something tied to the automatic transmission and tune associated with that??
I dont know how its just a torque converter instead of a flywheel attached to engine.

Does it only do it while the engine is cold?? Still sounds like air in system to me.

 

[DuraBioPwr]

You said injectors are stock right??

I put slightly larger injectors on a old 95 cummins and they 'should' have worked fine but it had an off idle stumble that never went away. Had to put different ones on it. Even the old mechanical stuff was touchy when something changed.