2.8 idle problem (Page 1/1)
pontiacfierokid1985 MAR 05, 11:59 PM
86 2.8 4 speed

Like post says I notice I got a weird idle going on. Now if I let the car warm up it will idle 2500 rpm which I know is way to high 1900 should be high idle on a dead cold motor. And 950 when fully warmed up. Tried figuring it out but said to hell with it. But I been noticing something else when it is fully warmed up it will idle around 1100-1200 rpm but if I drive it let in the clutch and just coast it will idle at 1500. Come to a dead stop for like 3-5 seconds it will idle at 1000-1100 rpm I’m wondering if the speed sensor has something to do with this. There is no cruise control hooked up in the car and the neutral safety switch has been by passed could these have any problems with it. If I do the ecm by pass and let it run to reset the iac reset the car will run at 1000 rpm all day long really confused about this. 🤔
Gall757 MAR 06, 09:55 AM
The VSS sends a signal to the ECM, which controls idle speed with the clutch disengaged and the car is moving. Perhaps your VSS plastic gear is mulched. The other possibility is a bad or incorrect chip on the ECM.

[This message has been edited by Gall757 (edited 03-06-2020).]

theogre MAR 06, 11:21 AM

quote
Originally posted by Gall757:
The VSS sends a signal to the ECM, which controls idle speed with the clutch disengaged and the car is moving. Perhaps your VSS plastic gear is mulched. The other possibility is a bad or incorrect chip on the ECM.

Wrong.
VSS is used only by Speedo board in Fiero.
Speedo board then drives ECM and Cruise if car has that.
So when the Speedo works then Is Not a VSS problem.

High idle when engine hot is often iffy vacuum part(s) or hoses/lines to them. See my Cave, Vac Leaks
Iffy power and/or ground(s) can make ECM to see low volts and cause high or hunting idle. Need a scan tool to read data stream for ECM. Even w/o such tool, Check/clean/fix + and grounds bolted to starter, block, etc. in engine bay @ minimum.

High idle w/ engine cold depends on above or not but ECT and others even working perfect will cause high idle for cold weather to prevent stalling until engine is hot.
Iffy ECT and MAT/AIT sensors or wiring to them can make ECM to see low temp all the time. Use ECM scanner or follow chart in my Cave, Sensors Quick Ref @ minimum. But follow charts often don't mean much because iffy old style ECT plug and wiring can cause ECM to read wrong even when temp sensors are good.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Gall757 MAR 06, 03:31 PM

quote
Originally posted by theogre:

So when the Speedo works then Is Not a VSS problem.




Does the Speedo work?
pontiacfierokid1985 MAR 11, 10:14 PM

quote
Originally posted by Gall757:


Does the Speedo work?



Yes the speedo does work. When I took the vss to see if the teeth were all messed up they looked perfectly normal I m thinking it’s gotta be a vac leak or something. I’m gonna be doing the intake gaskets soon anyway and be replacing any vac lines that I could since it will all be apart