I've got an idle surging problem with my 98 Z-28 A4. It started after I installed a set of truck heads and removed the AC, Heat, & Air bags. It only hunts for idle in Drive and Reverse. It will not do it in Nuetral or Park. This is why I don't think it is a Vacuum leak. I cleaned out the IAC sensor. That helped a little. Since then I filled up the gas tank for the first time in months and now its hunting for idle just as bad as it was before I cleaned out the IAC sensor. Im guessing that it is going to be computer related but I thought I would ask to see if anyone else has run into this problem.

Thanks Jeff

 

Ignition --> High Octane Table: Add 2 deg to all points 400 to 1000 RPM, .08 to .32 g/sec

Once done with this program, start the car and check for surging. If the car surges, unplug the IAC and see if the surging stops. If the surging stops follow below.

Idle Limiters --> Idle Air in Gear --> All points above 60C to 9.2

Take the car for a drive and check your idle. If the car goes on cruise control reduce the Idle Air in Gear Table .2 (further if necessary). If the idle holds at 2000 RPM for extended periods of time reduce the P/N Airflow Decay table for all points above 10 MPH by 5% (multiply by 95) until this stops. Be vary careful on this table.

If car keeps surging with the IAC unplugged two more things to try.

Multiply Main VE table by another 95% (total reduction of 85%). Repeat until the surging goes away, or until the car begins to hesitate when you take off.

High Octane Ignition Table. Reduce timing for all points 400 to 1000 RPM, .08 to .32 g/sec by 2. Repeat, but don't reduce it any more than 6 degrees.

If your car still doesn't idle after this, then you have other problems, and should start looking elsewhere.