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Rough Idle When Engine Is Warmed Up
Topic Started: Aug 9 2018, 11:17 PM (102 Views)
Dirty_Dan
Fresh Fish
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My 94 Geo 3 cylinder has a rough idle, mostly when it reaches operating temperature. When I start it in the morning it usually runs OK, but if I wait a few minutes or drive a bit the idle gets really shaky. The car only has 53,000 miles on it. I replaced the air filter, spark plugs, wires, distributor cap, and rotor. All of them needed replacement but none fixed the idle issue. I also cleaned out the EGR valve, which had a fair amount of carbon build up but nothing extreme.

If I give it a little gas the shakiness goes away and it runs good otherwise. One thing I consistently notice is that after work in the afternoon when the car has been sitting out in the sun a while, it idles buttery smooth, absolutely perfect. Then after I drive it a mile or two the idle gets progressively worse. Not sure if that is helpful but its something I've noticed. It doesn't seem to be overheating at all.

Any ideas on what the issue might be? :hmm
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Oscar'sPilot
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I'm having the same issue but with completely opposite scenario (rough idle only at cold starts). Do you have an OBD2 scanner to get a live data feed?
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freegeo
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Since you have a 94, do you know if you have standard emissions or up graded?
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freegeo
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Upgraded emissions will have a ISC on the back of the throttle body. Check the link for a picture of what it would look like.

http://geometroforum.com/single/?p=3076079&t=8330832.
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MR1 Kingsbury
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Exp. builder/rebuilder

prior to upgraded emissions they used IAC (or Idle Air Control) which is primarily an ECU controlled vacuum leak to promote a proper idle speed during cold starts and running temps... Seems strange that yours would run well cold then stumble into extra low idle after its warmed up. I have seen IAC get restricted and semi clogged with carbon and corrosion.
Edited by MR1 Kingsbury, Aug 10 2018, 07:51 AM.
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geogonfa
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Just my .02¢... :type
The first thing to check would be the Compression,
So you can make sure how healthy the engine is...

http://geometroforum.com/topic/2574993/1/
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nickb803
NickB803

I agree with the comp check. Does it idle like a diesel? If so comp check, timing check and vac leak check.
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Dirty_Dan
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Oscar'sPilot
Aug 9 2018, 11:57 PM
I'm having the same issue but with completely opposite scenario (rough idle only at cold starts). Do you have an OBD2 scanner to get a live data feed?


I could be wrong but I don't think they used those scanners until the 95+ models. Otherwise I would try the scanner and check. I don't have any warning lights on.

freegeo
Aug 10 2018, 05:29 AM
Upgraded emissions will have a ISC on the back of the throttle body. Check the link for a picture of what it would look like.

http://geometroforum.com/single/?p=3076079&t=8330832.


I'll double check tomorrow but I'm fairly certain mine does not have that part on the back.

geogonfa
Aug 10 2018, 08:13 AM
Just my .02¢... :type
The first thing to check would be the Compression,
So you can make sure how healthy the engine is...

http://geometroforum.com/topic/2574993/1/


I rented a compression tester, I'll try to test tomorrow. I'm in the middle of replacing the front struts at the moment. I remember the previous owner saying he tested one of the cylinders at 190 but I don't remember the individual readings for each cylinder, just that one.

EDIT: It does either leak or burn some oil. I have to give it about a quart per 1k miles. The underside by the oil pan gets pretty wet but even on concrete for a few days I don't see any sign of it dripping.
Edited by Dirty_Dan, Aug 10 2018, 10:33 PM.
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freegeo
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Your car would only need a spare fuse in the diagnostic slot on the junction block to check for codes.
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