Engine Surges when Idling
Thread Starter
Melting Slicks
Joined: Feb 2004
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From: Sarcasm. Just one of the many services I offer.
Engine Surges when Idling
When the engine is idle on my 86 the rpms go up and down by themselves, its as if I was lightly revving the engine....
Drifting
Joined: Oct 2004
Posts: 1,976
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From: Patchogue NY
Having a bit of that behavior with my 91 Coupe. Plan on doing a complete tune-up including the wires. If the tune doesn't resolve the problem, then I will explore the Throttle Position Sensor. Good Luck.
Joe B.
Joe B.
Intermediate
Joined: Aug 2004
Posts: 45
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From: Anaheim
I'm glad that you asked that question, because my '92 Chevy C1500 350 engine with fuel injection is kind of doing the same thing. I hope you don't mind my tagging along on your post (parasiting?) but maybe if we team up we can get more answers. When I'm sitting at a red light idling, I can feel the engine kind of fumbling but not necessarilly missing on a cylinder. I can also watch the tach and see the RPM's drop when the engine fumbles. It's erratic, so I know that it's not a spark plug, unless it's missing inconsistantly. When I accelerate at a normal rate, I get a little fumble, and then it straightens out and runs pretty smooth. If I go wide open throttle, it fumbles slightly, then accelerates smoothly with a lot of power. No missing, no backfire, none of the typical plug-wire-distributor symptoms. The truck doesn't have a MAF. The fuel injection looks more like a carburetor with two injectors spraying into the throat. It does have wires connected to the injectors, so I know that it's electronic monitored. 85,000 miles. No previous fuel injection service. I suspect that it's dirty injectors. What do you guys think?
Team Owner
Joined: Sep 2001
Posts: 62,139
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From: Athens AL
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Check TPS voltage, clean the TB and IAC. Check for vacuum leaks.
If it was doing it at normal temperatures, then I'd inspect the EGR as well.
If it was doing it at normal temperatures, then I'd inspect the EGR as well.
Intermediate
Joined: Aug 2004
Posts: 45
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From: Anaheim
My '85 Vette does a little wandering too, but not enough to bother me. Your '86 could even have a leaking vacuum line somewhere on the engine. I replaced as many of my vacuum lines on the '85 as I could find and that seemed to smooth it out a little. It idles at about 600 RPM.
Racer
Joined: Mar 2004
Posts: 311
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From: Oakley Ca
If all else fails, increase the idle speed a little bit. The idle is a little slower than the ecm wants it to be, so the iac is opening a little to get the idle back up where it should be. The head on the idle set screw is hidden under a plug that has to be removed. Needs a small torx driver to turn. Or grab the end of the set screw with some vise grips to turn it out a little. Worked for me.
Intermediate
Joined: Jan 2005
Posts: 36
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From: Clearwater Beach Fl
Originally Posted by olman
If all else fails, increase the idle speed a little bit. The idle is a little slower than the ecm wants it to be, so the iac is opening a little to get the idle back up where it should be. The head on the idle set screw is hidden under a plug that has to be removed. Needs a small torx driver to turn. Or grab the end of the set screw with some vise grips to turn it out a little. Worked for me.
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Pro
Joined: Jul 2004
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From: 1985 L98, Auto. O'FALLON, IL
Guys, my 85 had a surging idle last summer, I got alot of advice from the forum. 2 places to check. first you can check your fuel injectors with an ohm meter, they all should be around 17 ohms. second get the car warmed up and then disconnect the O2 sensor, if the hunting goes away replace the O2 sensor. I bought a Bosch at Advanced Auto for about 25 bucks. At idle the car does not surge anymore, however I am still not convinced the car idles as good as it should. I have a feeling that it could be the fuel injectors and that there is more that can go wrong with them than a resistance check will show. I recieved a tpis catalog on friday and they have a test bench that will match them up for 15$ a piece.
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
Originally Posted by onetrackmind
Guys, my 85 had a surging idle last summer, I got alot of advice from the forum. 2 places to check. first you can check your fuel injectors with an ohm meter, they all should be around 17 ohms. second get the car warmed up and then disconnect the O2 sensor, if the hunting goes away replace the O2 sensor. I bought a Bosch at Advanced Auto for about 25 bucks. At idle the car does not surge anymore, however I am still not convinced the car idles as good as it should. I have a feeling that it could be the fuel injectors and that there is more that can go wrong with them than a resistance check will show. I recieved a tpis catalog on friday and they have a test bench that will match them up for 15$ a piece.
I was also thinking O2 sensor(s). I like the idea of disconnecting them to see what effect it has on idle...... If you are interested, here's a short tutorial on how the ECM uses the O2 sensors output to adjust for "lean" and "rich" conditions:
http://www.ngkspark.com.au/tech_info...sors_index.htm
Last edited by MikeC4; Feb 13, 2005 at 08:29 PM.
