99 with new plugs & wires – no codes – runs great – smooth at idle when at 700

Starts and idles fine – after warm up idle drops from 700 to 400 and sometimes will fluctuate slowly
When pushing in clutch at stop light, idle goes to 400 and sometimes the engine stalls
If it doesn’t stall, sometimes idle will go to 700 on its own

I’ve checked the visible vacuum lines – the PCV was recently replaced

Any suggestions on what to look at next?

Thanks

 

The first thing I would try is cleaning the throttle plate and the MAF sensor.

 

1) Insert key into ignition and turn to the “ON” position, but, DO NOT START THE ENGINE.
2) Open the engine compartment fuse box cover and remove the two 10 amp fuses from position numbers 16 & 23.
a) According to the manual there are two fuse boxes. Use the engine compartment fuse block for this procedure not the instrument panel fuse block.
b) Engine Compartment Fuse Block (correct one): 16 is Powertrain Control Module A and 23 is Powertrain Control Module B.
c) Instrument panel fuse block (wrong one): 16 is Air Bag, 22 is Body Control Module-Ignition and 23 is Body Control Module-Ignition 2.
NOTE: Your DIC will now display “check” messages for ABS, etc… Do not worry as this is normal.
3) Turn the ignition key to the “OFF” position.
4) Return to the engine compartment fuse box and re-insert both 10 amp fuses for positions 16 & 23.

5a) Idle relearn for an M6:
1) Start the engine and allow the coolant temp to reach a minimum of 176 degrees F. Allow the engine to run at this minimum temperature for at least 5 minutes.
2) After the 176 degree, 5 minute minimum run, shut down the engine for a minimum of 30 seconds.
3) Restart the engine and check for DIC error codes (there should be none).
5b) Idle relearn for an A4: (different)
1) Start the engine and allow the coolant temp to reach a minimum of 176 degrees F. Allow the engine to run at this minimum temperature for at least 5 minutes.
2) Allow the car to idle in DRIVE, with air ON and then OFF, for 5 minutes each, and then in NEUTRAL, with air ON and then OFF, for 5 minutes each.
3) Turn the car off for at least 30 seconds.
4) Restart the engine and check for DIC error codes (there should be none).
6) Drive car for a minimum of 30 miles at varying rpm settings and speeds. PCM will now re-learn and adjust for the new air flow and temperature at the intake.
a) If error codes persist, repeat steps 1-7. Make sure fuses are properly inserted before repeating steps.
b) Do not deviate from the sequence outlined above. If you do, restart the sequence from scratch.
c) Steps 1-4 are also necessary if you ever disconnect your battery or lose power for any reason.

 

Yes, I tend to agree with the idle relearn but first make sure the air bridge isn't leaking unmetered air into the intake. A lot of times, the bottom of it comes off. You said you already checked the PCV therefore will assume the connection tube from the PCV valve to the intake was good as well.

 

THANKS for the help!

I'll do the additional check then do the re-learn

Thanks!

 

Did this fix your problem? Just curious, I have a very similar issue. I tried all of these fixes without success. I'm pretty sure it's in the tuning now, but still curious how you made out. Thanks

 

Hey,
Good question?
I did the re-learn procedure .... no effect at first but without making any other changes after about 2 weeks the idle returned to almost normal .... steady at 600-700 instead of 400 but will at times hold at 700.... at least it doesn't stall any more .....

This has been hard to find/fix .... the last time I had an idle problem it was the hose going into the EGR .... but that set a code which made it a piece a cake to find ......

Good luck finding your problem!

Let me know what it was ....

 

I take it this was not on a C5...

 

No, 99 C5
Why?