My 1991 Chevy Silverado starts up ok, but has a rough idle until it warms up. Once it is warm, it runs good unless you try to accelerate real fast. It then bogs and backfires

5

Asked by May 04, 2017 at 11:52 AM about the 1991 Chevrolet C/K 1500 Scottsdale Extended Cab SB 4WD

Question type: General

My 1991 Chevy Silverado starts up ok, but has a rough idle until it warms up.  
Once it is warm, it runs good unless you  try to accelerate real fast.  It then
bogs and backfires thru the Carb and exhaust. Have replaced plugs, PVC
valve, cap and rotor, MAP sensor, O2 sensor and exhaust pipes.  When I
accelerate real fast, it backfires and then takes off.

1 Answer

73,035

It may be the idle air control valve is all plugged up. It is on the passenger side of the TBI, square plug. Should probably take the IAC valve out, then take the TBI off and clean it up good along with the port for the IAC valve. Then you can check the base gasket at the same time as they will go bad. Once this is done then see what it does. It may be that the fuel regulator in the TBI is needing to be replaced. Fuel pressure should be 9 to 13 lbs. Check with a gauge and rev the engine up to see if it holds fuel pressure within the range.

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