Posted: 4/24/2012 7:11:39 PM EDT
| 97 Cavalier 92K. Auto trans. Engine will stumble only in drive w/ brakes on. Otherwise fine... Any ideas on what this could be? Want to DYI preferrably. I am handy but lack in the diagnosis department. |
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Only in drive? Not reverse or any other gear? At idle, drive only. Not tried reverse. Assume it does for my question. I don't want to overlook any possibilities. Vacuum leak To test grab a can of carb cleaner and spray around vacuum lines, if engine revs when a connection is sprayed it is leaking. Also you can use a stethoscope to listen around the engine for air hisses. |
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Quoted: Quoted: Only in drive? Not reverse or any other gear? At idle, drive only. Not tried reverse. Assume it does for my question. I don't want to overlook any possibilities. The engine still has the full power range while driving, but wants to stall when in drive and stopped? |
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Neutral drop it a few times while holding the parking brake. Should fix the problem. make sure to shoot video. thank me later after you got 30 million hits on yutube 
If I dont get this corrected Ill run a mag or three thru this at it,,,,That will fix that piece of shit right up. 
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Only in drive? Not reverse or any other gear? At idle, drive only. Not tried reverse. Assume it does for my question. I don't want to overlook any possibilities. The engine still has the full power range while driving, but wants to stall when in drive and stopped? Correct. Acelleration from a stop and it will stutter as well. BUT not all of the time. Just occassionally. |
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Only in drive? Not reverse or any other gear? At idle, drive only. Not tried reverse. Assume it does for my question. I don't want to overlook any possibilities. Vacuum leak To test grab a can of carb cleaner and spray around vacuum lines, if engine revs when a connection is sprayed it is leaking. Also you can use a stethoscope to listen around the engine for air hisses. My initial thought as well, with the limited data. |
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If it does it with the brakes applied, look for a vacuum leak on the power brake booster. Disconnect (and plug) the vacuum line to the booster. If the problem goes away, you found the source of your vacuum leak. 
This was going to be my guess. Vacuum leak will cause the problems you describe. Get a spray bottle of diluted soap solution and spray the hoses/fitting to determine what is leaking. |
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Only in drive? Not reverse or any other gear? At idle, drive only. Not tried reverse. Assume it does for my question. I don't want to overlook any possibilities. Vacuum leak To test grab a can of carb cleaner and spray around vacuum lines, if engine revs when a connection is sprayed it is leaking. Also you can use a stethoscope to listen around the engine for air hisses. This. You have a vacuum leak. Make sure your oil cap is on and tight, then start checking hoses. |
| Vac leak but ONLY if it does it in reverse also. a vac leak would affect it when in gear. Also maybe a fuel filter, since when in gear the engine is under load and requires more fuel. If the filter is dirty it will restrict fuel flow. Also possibly a dirty idle air control (IAC) valve. |
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Vacuum leak Good call. The fact that it only stumbles when the brakes are applied is a clue that the leak may be in the brake booster. For confirmation, try disconnecting the vacuum hose from the brake booster, plugging it so that the engine can still develop vacuum. (You can zip-tie a plastic bag around the hose to temporarily plug it). If the engine no longer stumbles when you press the brake pedal, the booster is almost certainly the culprit. |
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At idle, in gear or not, foot on the brake or not, this year vehicle is running in open loop, ie: its putting fuel to the system at a preset rate. If there was a vacuum leak the O2 sensor(s) would report a lean condition, throwing a CEL code. No CEL code = not an engine problem (likely)
, or a selectively faulty ECU(much less likely). OP, let us know what you find out. My money is on the tranny, but I'm a shitty gambler. Edited |
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At idle, in gear or not, foot on the brake or not, this year vehicle is running in open loop, ie: its putting fuel to the system at a preset rate. If there was a vacuum leak the O2 sensor(s) would report a lean condition, throwing a CEL code. No CEL code = not an engine problem (likely), or a selectively faulty ECU. OP, let us know what you find out. Roger that. |
| IAC (idle air control) motor probly has alot of carbon built up , this will give you idle problems. has to be taken off and cleaned at the tip and where drives into . its a black round motor at the throttle body , and has 2 screws mounting it to the side of the throttle body. |