I keep hearing that a bad VSS will screw up your idle. Does it?
And will there be any other symptoms or a way to test this thing?

The speedometer works fine, but the cruise control has stopped working. I haven't checked fues yet for that though.

[This message has been edited by fierosound (edited 05-14-2002).]

welll....a VSS is the vehicle speed sensor...and it operates the speedo, so if your speedo is fine, chances are, the VSS is too now...the IAC would screw up an idle...so would the PCV, or some vacuume lines, or some sort of intake gasket, or any other number of things.

A bad TPS (throttle position sensor) will cause a goofy idle. The IAC (idle air control) is what controls the idle. A bad or gunked up one will screw the idle up, too.

------------------
"Its a Fiero thing... Heck, even I don't understand!"

Timothy E. Smith
1986 SE V6 BACK ON THE ROAD AGAIN!!!!
1984 Coupe
1996 Ford Probe GT
1999 Chevrolet Silverado Z71
1975 Chevrolet ElCamino SS

I know I'm grasping at straws now...

I've got new MAP. TPS, IAC, steel vacuum lines, everything else mechanical checks out OK. Jumping the A/B connections in the ALDL port puts the engine into "Field Test Mode", engine smooths out and purrs like a V8. NO CODES.

With WinALDL I don't see anything obviously wrong (jumping sensor outputs etc.) and everything look fine. I'm at my wits end!! GM techs aren't much help. Because the engine is 8 feet futher back from the headlights than other GM vehicles, I have a "UFO" and they can't work on it.

Thanks guys, any other ideas???

With out much info, how about O2 sensor, MAT sensor, if its v6 how about EGR tube or the EGR itself. Lots of possibilities here. here just gotta keep checking.

[This message has been edited by afRaceR (edited 05-14-2002).]

A few other of the wall things that can in some rare cases screw up the idle are:

1. overcharged ac
2. altenator not charging correctly

Also make sure you read west coast fieros article on idle speed. I wil have to find the link for you.

RossT brings up a very good point that can be expanded on.
Charging system, from alternator to battery to cables to grounds. I had a rough idle for awhile and couldn't figure out what it was, sometimes spit and sputtered at higher RPM's. One of my battery terminals had broke and was causing low voltage.
A healthy electrical system is a must on a Fiero, I think there is even a TSB about this.

If I remember, he has a 3.4 modified. One of the most beutiful cars on the forum!!

Logic would dictate that the first thing to check for would be a vacuum leak at the cruise control vacuum solenoid located on the vacuum canister, and its associated vacuum lines.