buccicone

Since putting together this project which we obtained with the intake apart, a refresh was done with all new vacuum lines (Roger's Kit), ISV, all hoses, it has intermittently idles at 1200-1400 rpm. We have checked the usual suspects, Temp II sensor, throttle switch (clicks properly), accelerator rod to throttle body. Today we switched out the MAF with a known good unit. No Joy. I know the first response is to check for vacuum leaks. As far as we can tell with spraying WD-40 around the intakes, there are no vacuum leaks. Up to last week it was idling in the 750 rpm range rather steady. The first long trip of 35 freeway miles and exiting the highway it kicked up to the 1200 rpm range and now has stayed there. The only smoking gun seems to be around the MAF when jiggled. Yesterday it settled to 750 rpm and stayed there quite a while until I boosted the speed at the pedal to 2000 rpm for 30 seconds and settled at 1200 rpm again and would not correct itself. Jiggles some more and NO change. Disconnected the ISV, NO Change. The idle screw on the front of the throttle body is turned all the way in. Have cleaned the grounds under the FPR's in the back of the engine.

Have we missed something or didn't thoroughly test some component ?

hlee96

My 86.0 5 spd is also doing the exactly the same thing and sometimes it would improve after "blipping the accelerator" at a stop light. Stan helped with checking the fuel injector o-rings, throttle quad, ISV, and returned the PO's AFM and o2-sensor back to original. It was "fixed" for several drives, but in the past week, after it's warmed up, it's idle speed is back to 1200-1800.

He is going to ship out my LH/EZ computers to have them checked.

Hopefully we will find out what's truly going on.

byrdman454

I would swap the ICV to see if you get a change. My nephew's '85 has been through at least 3 of the "aftermaket" ones and the only one that seems to last is the Bosch. It seems like everyone else has good luck with the "aftermarket" ICVs but not this car. The Bosch ones are NLA. I ended up buying a used one off eBay with a 12 month warranty and so far so good. It is not hard to swap out to see if that is your problem.

buccicone

The ICV/ISV has been switched from a Bosch to Aftermarket. The original Bosch had smooth operation as I can see. Disconnected the ISV electrical connector. No change. I believe the idle is so high it is out of the range for the ISV to control idle.

buccicone

Hoi, keep me posted. Sounds like we have similar issues. Ran great when idling correctly. Replaced O2 sensor also with Bosch OEM, Injectors were clean/rebuilt/replaced with the intake refresh. I think the LH/EZ will also need to be checked/rebuilt. Today going to check the MAF plug since some of the irradiate idle shows up with jiggling around the MAF area

Tampa 928s

76FJ55

Also on the S3s remember that you can adjust the base idle speed with the bypass screw on the front of TB, 7mm socket and extension IIRC.

buccicone

Done that. Turned all the way in. Did this on the initial (first run) after intake refresh. Got it about right 800 rpm but I know it should almost stall turned all the way in. My suspicion was something is not right then now it's really f**k.

buccicone

Question: When the ISV is a rest (no voltage applied), is the valve open or shut?

buccicone

I did read this thread: https://rennlist.com/forums/928-foru...gh-idle-4.html

76FJ55

Yes, it seems you've had an issue since the reassembly if you've closed off the ICV and couldn't get the idle below 800 with the idle bypass screw. The ICV is only able to increase the speed over the base idle setting, it will never be able to slow the engine.

bureau13

I've got a very similar problem on my '86.5, but the fact that you were able to see it idle more or less correctly for a while, and then it increased again after messing with the throttle makes me wonder if you're really in idle mode when you think you are. I would try this: Start the car, see that it's idling high. Shut it off without touching the throttle. Disconnect the LH (or EZF, I forget which) and measure that your idle switch is reading correctly.

davek9

With a Replacement ISV in-place, if issue continues you need a new LH, the ISV control circuit is failing when warm/hot,

Dave K

928S MN

When you put in the new MAF, did you also replace the seals/gaskets?

Asking this because when I did the upper refresh, the old seals/gaskets were rock hard. Not unexpected after 30 odd years of service. Before doing this I had exactly your problem.

buccicone

With it running, we put in the original ISV outside the system and it IS pulsing (without connecting the hoses to check the electronics to the ISV). With the replacement mounted, no change in RPM with the connector disconnected. Conclusion: Got power to the ISV. Is it the correct Power?