ra thump ra thump from ip, rough idle, iq fluctating

ra thump ra thump from ip, rough idle, iq fluctuating

A customers very clean, 97,xxx mile, 2002 jetta tdi on which I changed the tb last week, and today new nozzles. I had never heard the car run until after the tb. Now, at idle an intermittent rough idle combined with a cyclical ra thump ra thump kind of noise seeming to come from the ip, combined with the iq going spaz on vag-com happens simultaneously. When it runs poorly, iq fluctuates from a reasonably steady and normal 3.6-3.8 to 3.0-4.8, but timing never changes, rpm fluctuates from 903 down to 885'ish. Strange, yes. Stranger yet is when you depress the clutch pedal, the engine normals out immediately. Keep the clutch depressed, the intermittent rough idle never occurs. Timing is perfect of course, and I checked the pressure relief valve. No smoke ever, the car runs fine otherwise. Something to do with the crank shaft walking maybe ? Debris on the crank position sensor ? Full moon ? Any ideas on this one ? Thanks.

I would say bad grounds by instinct... probably in the rain tray or on the engine main ground... or maybe an injector/glowplug has a compression leak???

I recall someone mentioning pulling the crank sensor and seeing if the speed wheel is loose. Also, pull the inspection plug for the timing mark and see if the flywheel itself moves. And take a look at the oil for any obvious metal contamination.

Wild guesses, yes; but to me, this is a head scratcher.

Broken DMF. I bet a $10 donation to the club on it

noob question...whats a dmf?

DMF = dual mass flywheel - Jack up the car and lying under it rotate both wheels forward and reverse while in 1st gear. If you get alot of compliance in the drivetrain and some clunking check the dmf flywheel. (engine/key off of course). Knocking in the pump could be the drive coupler failing.

Jeff

jsrmonster said:

DMF = dual mass flywheel - Jack up the car and lying under it rotate both wheels forward and reverse while in 1st gear. If you get alot of compliance in the drivetrain and some clunking check the dmf flywheel. (engine/key off of course). Knocking in the pump could be the drive coupler failing.

Jeff

Click to expand...

If I see the car again today I'll check that. I'm most confused though in how the clutch being depressed has any relativity in returning the engine back to running normal. The noise I suspect is coming from the pump disappears instantaneously as well. If the dmf is failing, is it failing in a manner that is dragging the engine performance down to such a point the ecu is trying to get it normaled up again, thus the fluctuating iq and idle ?

Play in the DMF can affect the signal from the crank position sensor, I believe.

jsrmonster said:

DMF = dual mass flywheel - Jack up the car and lying under it rotate both wheels forward and reverse while in 1st gear. If you get alot of compliance in the drivetrain and some clunking check the dmf flywheel. (engine/key off of course). Knocking in the pump could be the drive coupler failing.

Jeff

Click to expand...

If the DMF is failed, the flywheel mass can flop hither and yon randomly which will speed/slow the engine slightly causing the injection pump to try and respond, adding fuel as it gets the slow down of the engine, then turning it off as it over speeds slightly, rapidly.... I concur, you've got a porked DMF, pump noise is probably a byproduct of the DMF. Verify using the procedure above...

concours said:

If the DMF is failed, the flywheel mass can flop hither and yon randomly which will speed/slow the engine slightly causing the injection pump to try and respond, adding fuel as it gets the slow down of the engine, then turning it off as it over speeds slightly, rapidly.... I concur, you've got a porked DMF, pump noise is probably a byproduct of the DMF. Verify using the procedure above...

Click to expand...

OK, This one makes sense. I also like the use of "hither and yon", so I'm now with everyone else on the DMF.

What is the IQ when then engine runs normally with no clutch? And with clutch?

I'll bet you can solve your problem by raising the IQ less than one full point above its current average.

runonbeer said:

What is the IQ when then engine runs normally with no clutch? And with clutch?

I'll bet you can solve your problem by raising the IQ less than one full point above its current average.

Click to expand...

When it runs poorly, iq fluctuates from a reasonably steady and normal 3.6-3.8, to 3.0-4.8. Before I adjusted the IQ, it was set at 1.2.