gremlins!

84FieroDude · Post by **84FieroDude** » Wed Sep 12, 2007 6:56 pm

I have a 1984 Fiero with a 4 cylinder engine. It runs great, except the idle will go really high (around 2500+ rpm) for no apparent reason.

I have checked the injector while it was running, and it goes from a fine mist at a low idle to revving like crazy and spewing gas. The only code it gives is for the coolant sensor. I just recently replaced the O2 sensor and have disconnected the IAC while it was running; neither affect it.

Any suggestions why it would be doing this and how to fix it?

Series8217 · Post by **Series8217** » Wed Sep 12, 2007 7:13 pm

Is the idle always very high, or just sometimes? If it is constantly high you have a vacuum leak. Otherwise something funny is going on with the IAC or the IAC control circuit. The ECM itself could be the culprit.

Just a note, this thread will get moved to the Maintenance section where it belongs, so look for it there if you can't find it.

befarrer · Post by **befarrer** » Wed Sep 12, 2007 8:14 pm

Have you replaced the coolant sensor? If the engine sees a very cold engine (like when the sensor is unplugged), it will increase the idle to some very high RPM like 2500 on the 4 cylinder.

Mach10 · Post by **Mach10** » Thu Sep 13, 2007 11:59 am

Check to make sure the throttle actually closes when you take your foot off the pedal.

It's an old car, with old cables, and an old throttle return spring.

Tap the throttle, see if it settles back down, or grab the linkage arm .

My car needed an additional spring added, as the old one wasn't stiff enough to consistantly close the throttle fully.

84FieroDude · Post by **84FieroDude** » Thu Sep 13, 2007 6:04 pm

Thanks for all the suggestions! befarrer was right on the money.

It turns out that a previous owner's shoddy repair job allowed the live and ground wires in the coolant switch to touch

, so it the ECM thought the engine was always cold. Easy repair.

Runs perfect now!

befarrer · Post by **befarrer** » Fri Sep 14, 2007 1:30 am

:thumbleft: Yay I win :bootyshake:

Almost every duke revs to over 2000RPM when first started up for a few seconds, untill the temp starts rising. Sucks when you have an auto like me, you have to wait for the stupid thing to warm up and idle down before putting it in gear, or else it is like doing a neutral-drive dump, and spin the wheels everywhere.

Aaron · Post by **Aaron** » Fri Sep 14, 2007 4:21 pm

befarrer wrote:and spin the wheels everywhere.

Can a Duke even do this on ice?

p8ntman442 · Post by **p8ntman442** » Fri Sep 14, 2007 6:45 pm

in my grand am with a duke, I could keep the tires spinning all day doing a neutral drop on a steep hill. 195/60/r15's