High Idle, slow to return to normal
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Joined: Apr 2006
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From: Maine
High Idle, slow to return to normal
Hello, My 1987 is acting up by not returning to normal idle. Will idle as high as 2000 RPM steady until I punch the throttle and then it will drop down to 700 or 800 RPM. Happens pretty consistently. I've lubed the throttle mechanism and it seems to work freely. I suppose it could be cable binding. The car runs fine and is smooth, so I am not convinced it is the TPS, though certianly could be. Also, the car commonly starts hard after warmed up, taking two or three times to fire up and ussually needs some throttle help to do so. Any thoughts? How would I check or lube the cable ? Thanks, Steve
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Joined: Apr 2006
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From: Maine
Thanks. Idle air control, as I understand a fault with it, would commonly not have such a high idle proble, normally closer to 100 to 200 off, rather than 1000 off. Good thought though and still possible. I don't have a code reader for this car, only an OBDII. As for the recommendations about air leakage and "blades" hanging up, what are the blades you are referring to? I did hit the throttle shaft with WD 40 and did notice some deterioration in idle for a minute or so. Are the bushings replaceable or will I need a new Throttle body? Also, why would a punch to the throttle bring the idle back to normal. Feels like my old 69 Camaro with a sticky linkage ! Thanks, Steve
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Joined: Apr 2006
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From: Maine
Only 51k and the car has been very well cared for, most recently by a local Vette specialty shop. It's a problem that has been sneaking up on me since last year, but is very acute last few times I've driven the car. I only drive it a couple thousand miles per year. Thanks, Steve
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Joined: Aug 2006
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From: Milltown NJ
This spring I had a surging idle once the car got warm on my 88. She was fine until computer went to normal mode, then progressively got more out of line. Not sure if the same problem, but on mine a new o2 sensor cured it. I had codes thrown once it got real bad though.
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From: Maine
Cleaned the throttle body today and ran the car ( hard). Aside from being a ball, I still have a nagging high idle, though not as high as yesterday . Tends to hang up around 1200. I can still give it a quick punch and she'll drop down . There is a very slight surge to the idle (1-200 RPM fluctuation occasionally), but hardly as bad as most cars that like to "hunt" for idle. Could be vacuum or another air source. Time for a pro to look at it. Every time I get ready for winter storage here in Maine, something crops up. She doesn't like to go to bed. Thanks for all your help. Steve
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From: Maine
Took the car to the service tech today. No codes noted. They checked all the ussual items, but could not find any faults. A leakdown test on the fuel system did fail and he felt it could be a leaking injector. I picked the car up after they closed and it still idles too high , not all the time, but often. Now tends to stick around 1200rpm. Quick throttle bursts bring it down. The tech suggested I check under the dash to be sure the linkage is free and clear. I'll do that tonite. I do notice now that the normal idle hunts more than in the past , fluuctuating between 600 and 1100. Never wants to stall, but erratic. Other than all this, the car runs smooth and strong. I'm perplexed. Any reaction to manifold temperature sensor failed or failing? Would a poor injector boost idle to a smooth 1200rpm? Hate to put it away not just right. Thanks, Steeve
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Joined: Sep 2005
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St. Jude Donor '07
I am experiencing the exact same problem. Usually a high idle with occasional surging between 700 & 1400. Then there is the feeling that it is occasionally cutting out for a moment.
Things I know it is not:
IAC - New
ECM - New
MAF Burnoff Module - New
MAF - New
TB - New
Exhaust - New
Vac Leak - Checked in all manner of ways.
Cap/Rotor/Wires/Plugs - New
Linkage bind - Checked carefully.
Thinking:
Leakdown fail, though the injectors ohmed perfct when cold.
Canister system fault. Maybe purge valve is malfunctioning.
Ground issue.
Short.
Pick-up coil, though it tested properly.
EGR not seated properly every time.
Other ideas?
Things I know it is not:
IAC - New
ECM - New
MAF Burnoff Module - New
MAF - New
TB - New
Exhaust - New
Vac Leak - Checked in all manner of ways.
Cap/Rotor/Wires/Plugs - New
Linkage bind - Checked carefully.
Thinking:
Leakdown fail, though the injectors ohmed perfct when cold.
Canister system fault. Maybe purge valve is malfunctioning.
Ground issue.
Short.
Pick-up coil, though it tested properly.
EGR not seated properly every time.
Other ideas?
Le Mans Master
Joined: Jul 2007
Posts: 5,043
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From: Tampa Florida
I think your on the right track if the IAC checks out OK. With the car doing its "high idle thing" check to see if the throttle body blades are shut against the stops (push back on the bracket see if the cable is binding).....if it moves it is binding ....replace the throttle cable or add an extra spring that will compensate for the bind.
Below is a photo of an extra throttle body return spring (accordion style) I installed on my '89 to fix an internal cable binding problem. The spring(painted black and looks like a tube)is located in the center of the photo under all the dirt....ignore the bolt laying on the intake.
Below is a photo of an extra throttle body return spring (accordion style) I installed on my '89 to fix an internal cable binding problem. The spring(painted black and looks like a tube)is located in the center of the photo under all the dirt....ignore the bolt laying on the intake.
Pro
Joined: May 2006
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From: Pittsburgh PA
You said you checked for a vaccum leak. But it sure sound like one to me. Check your PCV valve and hose closely. I saw a PCV hose that had a crack in the inside of the 90 degree bend. It was not seen vary easily or did it leak badly until the engine heated up. Did you perform your leak check with propane? Good luck. Jack
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Joined: Apr 2006
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From: Maine
Jack, I don't know what he used to check for vacuum leaks. He described a "spray" they use. I've not heard of propane used before. Hows that work? I'll check the PCV valve and hose. Good thought. Its definitley an issue that worsens as the car reaches operating temp or is run for some time. May require a closer look by my Vette specialty guy, but he's 2.5 hours away. Not easy to coordinate, but the shop is class A. I'll keep working on it. Steve
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Joined: Jun 2001
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From: Orlando FL
St. Jude Donor '08-'09
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Joined: Apr 2006
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From: Maine
My 87 doesn't have a chip in it. I did notice today that on fast idle I could push back the throttle at the TB and reduce the idle. I'm now suspect that the TB may need a thorough cleaning or even an additional return spring. More to work on. Steve