Art20c

87 928 s4, auto
when i start engine, sometimes idle jumps up and down, when i hit gas, sounds like out of gas, stalls. engine misses, misfires.
then its ok.
when idle acting up, disconneced plug on throttle body, idle stabilizes right away. unable to rev though. as soon as it connected back, starts same story. Also, while its runing w/o filter housing if i hold my palm just over throttle body not even touch it just little airflow restriction, it starts running ok. what this plug controls?

fabric

You're talking about the cylindrical deal with the electrical connector on the drivers side? MAF. Sounds like it might be on its last legs. There's a whole slew of things that can cause idle problems, though:

*Vacuum to dampers and FPR off throttle
*Vacuum off throttle body to emissions valves
*false air getting in after MAF
*FPR or dampers might not be working right

These are relavitely easy to check, and could still be causing a problem even with the mucking with the MAF, although that sounds like the culprit. Could also be the LH brain.

Other things causing idle problems:

*ISV
*Temp II
*O2 sensor
*corroded grounds

In your case, probably try with swapping the MAF, then maybe the LH brain, but checking most of the above is free and easy, search will turn up how to do this, too much for me to write now.

If you can't tell, I'm working on an idle issue on my 87.

Art20c

thanks for info.
yes i ment maf. whats fpr and isv stands for?
where i can find all vacuum diags?

killav

I had this exact same problem. My problem/fix was that the rubber hose that runs from the Idle Solenoid Valve (ISV) to the rubber elbow below the MAF was disconnected. It had popped off the fitting that pops into the rubber MAF elbow. With the MAF unplugged, it defaults to a below xxx rpm setting, but won't rev very well. As soon as you plug it in, the MAF tries to read the incoming airflow, but gets nothing cause the air is by-passing the MAF, and my car would not idle on its own. I plugged my hose back on (a bitch by the way, must remove MAF to even stand a chance at getting to it) and this solved my problem. Can be many many things, but give this one a look as well. Your's wouldn't be totally disconnected since your problem is intermittent. But a leak anywhere on this hose will cause similar symptoms. Oh yea-FPR is Fuel Pressure Regulator.

Kore928

I agree with Mike. I had the same problem with that hose and it sounds like the same symtoms I had. My hose had a tear and I just went ahead and pulled the intake and did every hose and sensor under it. Car runs like a champ now.

Art20c

Mike,
is there any chance to check if that hose is leakig w/o ripping maf off
thanks
George

Kore928

Mine was obvoius because there was a slurping sound coming from underneath the intake. There is no way to get to it easily. If you're really sharp, you could possibly see a little bit of it from the front center of the intake with a flashlight, but that is still unlikely. Sorry I'm not much help. Just keep in mind that this is a good reason to refinish ( strip and paint) the intake.

Art20c

James,
i got same slurping noise w/o filter. with filter on, cant hear it

Kore928

The noise I heard was distinctly from the front of the intake, not having anything to do with the filter and only happened at idle when the idle valve was open. As soon as I revved the motor it went away. The hose in question simply bypasses the throttle body when the butterfly is closed. The valve is buried under the intake is the center. The hose goes from the idle valve to the rubber boot between the MAF and the throttle body and I think it stays mostly on the drivers side. Hope this helps.

Kore928

Do a search for John Pirtle's 928 Service website and click on "intake manifold". There are some really good pics and diagrams that might help you see what I'm talking about.