1992 Caprice idles rough and stumbles when in open loop

Tiny
CAPRICE9C1
  • MEMBER
  • 1992 CHEVROLET CAPRICE
  • V8
  • 2WD
  • AUTOMATIC
  • 22,500 MILES
I've got a tough one. My 1992 Caprice 9C1 with 5.7L idles rough and stumbles when the system is in open loop. Once the vehicle warms up it runs like a top. The exhaust tends to smell rich at most times. So far I have replace the Idle Air Control, Throttle Position Sensor, EGR Valve, MAP Sensor, Oxygen Sensor, all of the vacuum lines, Spark Plugs and Wires, Distributor Cap and Rotor, Coil, Module, Fuel Pump, and Fuel Filter. All have had little or no effect on the cars condition. The car has had this problem for some time and continues to occur even after my father and I put a used but newer motor in it last fall. The motor that was put in was the same size and type as the one removed. The car never displays a trouble code, and again runs fine once the car warms up and switches to closed loop. An interesting note, I happened to have a computer from an older model truck with the same motor, so I swapped that out with the car computer and it runs fine at all times. Thinking the computer was the problem I purchased another caprice computer and it went right back to doing the same thing. While the truck computer runs better, I would prefer to find the problem and be able to use the police computer that either came with the car or the additional one I purchased as it has better performance and fuel mileage. Thanks in advance for any suggestions anyone may have.
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Sunday, July 12th, 2009 AT 12:32 PM

2 Replies

Tiny
LOUT5369
  • MEMBER
Change the coolant sensor, It's telling your computer the engine temp is minus 32 degeeses when cold.
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Thursday, July 30th, 2009 AT 6:55 AM
Tiny
CAPRICE9C1
  • MEMBER
Changed the Coolant Temp Sensor and Intake Air Temp Sensor and reset computer with no change in the problem. The old one borderlined on its reading with an ohm meter so I changed it out, but it definitely did not cure the problem. Thanks anyways, but for now it is back to the drawing board.
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Thursday, August 6th, 2009 AT 10:36 PM

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