High Idle? (Page 1/1)
katie80 FEB 21, 01:27 PM
I have an ‘84 SE 4 speed and when i cold start it (at like 10F) it idles at almost 3k rpm. that is way too high. when i drive it a bit the idle settles down to a reasonable 1k. any ideas what would cause this? the throttle adjustment screw was messed with by a previous owner if that changes anything. thanks!
skywurz FEB 21, 02:55 PM
In my experience its a vacuum leak. Luckily there's not too many lines to check.
Spoon FEB 21, 07:09 PM
If somebody did tinker with the throttle set screw you should have it checked and reset properly. Years ago a member on this forum posted how the procedure is done. A deep search may find it if you're lucky.
Wait a minute here it is, your lucky day. A post from 3800superfast in 2007.

http://www.fiero.nl/forum/A...090219-2-080905.html

Spoon


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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

[This message has been edited by Spoon (edited 02-21-2021).]

AsaBergman FEB 21, 09:07 PM
84 4 speed here too. Cold start mine idles in the 2600-2700 for a bit then drops to around 1600 until it warms up and then drops to 700-800. If it's freezing out it may stay in the 2700 area for several minutes. It used to worry me but the car runs like new and gets great MPG. It seems this is normal for the 84 in particular and was changed in later years however if yours is staying around 3k I'd suspect a decent vacuum leak(as someone else said).

Definitely look into the idle screw as that shouldn't have been adjusted by previous owner, they were trying to fix a different issue the wrong way doing that.

Check on all vacuum lines to make sure they aren't cracked or loose. Check the hard vacuum line at the MAP sensor.

If properly setting the idle screw doesnt help I can give you a list of things to check as I'm very familiar with the 84.
theogre FEB 22, 12:50 PM
Some ECM are program to have high idle w/ engine cold in winter.
Many are high when first started and bump the gas pedal to slow some to a lot soon after starting.

Can check Engine Coolant Temp...

Get a ECM scan tool and read ECT report from ECM when engine is cold before starting. Plus Read/watch Weather or otherwise use local weather temp at minimum. Better, use IR or contact Temp to read engine.

Why?
ECT sensor or wiring could be iffy making ECM to see colder engine then really is.
If ETC sensor is replace older then 87 then must get new plug w/ new sensor and solder the wires.

See my Cave, Scan Tool Help etc.

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(Jurassic Park)

The Ogre's Fiero Cave

skywurz FEB 22, 01:04 PM

quote
Originally posted by katie80:

Iwhen i cold start it (at like 10F) it idles at almost 3k rpm. that is way too high. when i drive it a bit the idle settles down to a reasonable 1k.



Yeah I totally did not read right. I now agree this is to be expected when cold. If it stayed at 3k all the time I would say vac leak.