Stall on idle
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Joined: May 2003
Posts: 77
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From: Calgary AB
Stall on idle
I'm a fairly new vette owner and new to the whole injected computer car scene. Spent my younger years playing with 1st and 2nd generation Camaros.
Anyway I digress...
My 87 L98 auto started acting up after a WOT run on a country road.
It will run fine when over 1500 RPM, but under that it strugles, backfires and stalls.
I checked the codes, I had code 44 - Lean exhaust mixture @ O2 sensor.
I removed the fuel filter that I could barely blow through and put a new one in. Then replaced the throttle body to manifold gasket, and checked for ovbvious disconnected hoses/wiring.
I cleared the codes. I started it back up to find I have solved nothing (other than getting some required maintence done). I rechecked the codes - there were none.
It would seems to me this would be a vacuum leak or maybe bad timing.
Your thoughts...?
Anyway I digress...
My 87 L98 auto started acting up after a WOT run on a country road.
It will run fine when over 1500 RPM, but under that it strugles, backfires and stalls.
I checked the codes, I had code 44 - Lean exhaust mixture @ O2 sensor.
I removed the fuel filter that I could barely blow through and put a new one in. Then replaced the throttle body to manifold gasket, and checked for ovbvious disconnected hoses/wiring.
I cleared the codes. I started it back up to find I have solved nothing (other than getting some required maintence done). I rechecked the codes - there were none.
It would seems to me this would be a vacuum leak or maybe bad timing.
Your thoughts...?
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Stall on idle (DESPERADO)
A vacuum gauge will aid in checking for intake leaks; you can use the diagnostic method on my site to verify that the O2 sensor is ok and the ECM is going into closed loop with a stoch A/F.
You might clean the IAC under the TB and the TB; then reset base idle and the TPS value.
Also check base timing (first open the connector in the blk/tan wire near the brake booster) along with plug wires and plugs.
If you still have good power above idle I wouldn't worry about the MAF; the best test here is substitution (a MAF from a 3rd gen F-body works fine).
You might clean the IAC under the TB and the TB; then reset base idle and the TPS value.
Also check base timing (first open the connector in the blk/tan wire near the brake booster) along with plug wires and plugs.
If you still have good power above idle I wouldn't worry about the MAF; the best test here is substitution (a MAF from a 3rd gen F-body works fine).
Heel & Toe
Joined: Feb 2003
Posts: 20
Likes: 0
From: Greenfield IN
Re: Stall on idle (DESPERADO)
There is a check valve on the power brake booster that may have a problem. I have seen this before on other GM products. Just pull the vacuum hose off and block it off. See if that may be of any help. The brake booster only should use vacuum to replentish after the brakes are applied. if the check valve is bad it trys to consantly replentish the booster which in turn is a big vacuum leak.
Good luck
Tom
Good luck
Tom
Thread Starter
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Joined: May 2003
Posts: 77
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From: Calgary AB
Re: Stall on idle
Well, it's not the brake booster check valve. I haven't yet been able to do the checks 65Z01 has suggested.
It seems now that it's running rough at any RPM. :mad I'm hoping to get a timing light on it soon.
It starts beautifully, and runs well in the high speed idle circuit, but as soon as it starts running off the main circuit everything goes to poopie
[Modified by DESPERADO, 9:52 PM 5/22/2003]
It seems now that it's running rough at any RPM. :mad I'm hoping to get a timing light on it soon.
It starts beautifully, and runs well in the high speed idle circuit, but as soon as it starts running off the main circuit everything goes to poopie
[Modified by DESPERADO, 9:52 PM 5/22/2003]
Thread Starter
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Joined: May 2003
Posts: 77
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From: Calgary AB
Re: Stall on idle (DESPERADO)
OK I think I've got it!
I disconnected the air tube right after the MAF, but left the MAF electrical connected. The car ran fine, bit of a high idle 900 rpm, but it didn't stall or backfire.
I think this would mean my MAF sensor is FUBAR. Do you agree?
I know I should change out the burn-off relay when installing a new MAF sensor, is there any thing else that should be replaced?
I disconnected the air tube right after the MAF, but left the MAF electrical connected. The car ran fine, bit of a high idle 900 rpm, but it didn't stall or backfire.
I think this would mean my MAF sensor is FUBAR. Do you agree?
I know I should change out the burn-off relay when installing a new MAF sensor, is there any thing else that should be replaced?
Racer
Joined: Jul 2001
Posts: 253
Likes: 0
Re: Stall on idle (DESPERADO)
Hmmmm - a tube after the MAF? I'm going out to check mine on my '86. I've started getting some rough idle recently with a couple stalls. I've got the new spark plugs, cap, and rotor, but this is interesting to know.
I hope more info comes up on this thread.
I hope more info comes up on this thread.
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Joined: May 2003
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From: Calgary AB
Re: Stall on idle (86VetteBill)
Hmmmm - a tube after the MAF?
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Joined: May 2003
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From: Calgary AB
Re: Stall on idle (DESPERADO)
Well for those interested... My stall issue was caused by my MAF sensor. I tried my buddy's 86 MAf in my 87 and everything was working right again.
I'm buying the sensor from Bumper to Bumper, they had the best price and a 1 year warranty on the rebuilt model.
I'm buying the sensor from Bumper to Bumper, they had the best price and a 1 year warranty on the rebuilt model.
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