Question about 1998 GMC Jimmy
Remove the air intake assembly and take a look at the butterfly valve in the throttle body and make sure it is moving freely.The idle air controller or IAC for short could be making the idle drop too low as well.Check the wiring to the air flow meter on the air intake, and carefully look at the screen to make sure it is free of dirt.be careful,they are delicate and expensive.
The distributor could be bad,or a bad cap or rotor.
The grommet on the brake booster may be leaking,and when the brakes ar applied and use vacuum,it is creating a vacuum leak.Everyone seems to think that a vacuum leak always causes a high idle,but not so.Another thing is make sure there is no restriction in the exhaust system.Is there a rattle sound?a plugged cat converter will do strange things.
basically, start with the simple things, air cleaner filter,plugs, wires, cap, rotor, fuel filter.
check all connectors,vacuum hoses,and replace the pcv valve.
Then the IAC,air flow meter,map sensor and the distributor.
Posted on Mar 21, 2010
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