Doug Gennrich

I have an '87 S4 with a 180K. I recently purchased it and have a problem upon restart with a very erratic idle. The idle stabilizer and hoses were replaced by PO at 157K. Their was also a mention of a loose connection at the NTC connector that was fixed.

I also will comment that the idle is fairly smooth with only slight variation under normal conditions. Not perfect, Feel a slight vibration when idle speed changes maybe +/-50RPM in gear.

Any other recommendations. O2 Sensor? Vacuum Leaks?

khalloudy

Could be the MAF, that was my problem. check with a good one and see if it fixes the problem

Doug Gennrich

The car is a automatic and passes smog test no problem.

Car does not die but surges when hot start from 650-1500RPM hit the gas and it goes away.

Any other suggestions besides MAF

John Speake

Leaking injectors ?

airosey

Do you have a fuel pressure gauge installed? If so, check to see if the fuel system holds pressure for a few minutes after you shut the car off.

inokiyo

My 88 S4 had a similar problem. The only difference is that my would run rich when engine was warm/hot. See thread;
https://rennlist.com/forums/928-forum/271978-running-rich-and-rough-idle-when-engine-is-warm-follow-up-replaced-maf-and-worse.html
Have you pulled the plugs to see how it is burning? Mine was black with soot.
The problem was fixed with a rebuilt MAF and LH.
You might want to do some diagnositcs on the MAF and MAF which is listed in the above thread.
Good luck!!
Ken

abbzer0

How inconsistant is the idle? FWIW, I had an idle that moved up & down about 100-150 rpm's. When I changed to Shell Rotella 15W-40 all is good. Whatever the problem, best of luck.