Hey people I am new in this forum I need help pls throw some ideas...

1999 A4 1.8T/Q 5-speed and it has 115,000

Problem: The idle(rpm) goes up and down once a week or so and it reads between 400-1300rpm sudden bouncings and it wont stop until I stop the engine and turn it back on. This happens sometimes when I am on highway or local.

What I have Done: I checked almost everything sparks, plugs, gaskets, oils, filters, air hoses, coolant hoses, valves, coils, I have done my timing maint, oil change, I even cleaned the throttle. Turbo is stock but brand new, new gas cable, new belts and My clutch is also in good condition (checked by pros)

any ideas so far... thanks pple

 

most of the time it will be: a leak in the intake, bad MAF, or bad o2 sensor. with a boost gauge you would easily spot a leak. with vag-com you would be able to see if the MAF were bad.

 

i had a jumpy idle in my 98 2.8 and i noticed it would only happen on warmer days when the A/C was off, kinda wierd but hasn't been to much of a problem for me to investigate further

 

Did you clean out the throttle body really good?
have you tried a throttle body alignment?

 

could be the ICM going out.

 

Check engine light or codes?

 

Don't forget the IAC valve cleaning with the throttle body cleaning.

 

I cleaned the throttle body there was no change
There are no codes shown on the reader and my ICM is new too.
Plus I took my car to an inspection center even their computer couldn't find the problem.

Thank you guys for the ideas....but I still have to find the reason

 

try a throttle body alignment, if you have not already.
Disconnect the battery for a minute or two.
Hook it back up, and put the key in the ignition, and turn it to the on position but do not start the car.
Wait about 60 seconds or so. You'll hear the TB going through it's alignment process while you wait.
If you haven't tried that, it may help.
Good luck.

 

Shot in the dark (other than throttle body calibration): Bad cam sensor. Sometimes, they can cause random bouncing idle