Idle problem and problems starting after hot

TXSHERIFF

MEMBER
1992 CHEVROLET BLAZER
4.3L
6 CYL
2WD
AUTOMATIC

Howdy! I'm new to this forum stuff so please be patient with me!
I have a 1992 Chevy Blazer 6 Cylinders 4.3L CPI.
When I first got this truck 6months ago I had zero problems, here recently the idle on the truck would be at 2000rpms and stay there while in park, and when I placed it in drive, the truck would jump and accelerate on its own.
The fastest it has gone is 33mph! Keep in mind I'm not pressing on the gas.

Also yesterday it has started to not start after I drive it for 30mins, I have to let it cool down for it to start up again.

Things I have replaced-fuel filter, air filter, bleeder hose, spark plugs, wiring for spark plugs, cleaned distributor, tested ICM at auto zone and it passed, brand new IAC valve

any help would be greatly appreciated! I know this problem is probably a simple one!
Thanks

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

Idling too fast is typically caused by a vacuum leak. Failure to start when hot is usually the result of a failing sensor that has become heat-sensitive. The place to start is by reading the diagnostic fault codes. If there's one set related to the crankshaft position sensor or camshaft position sensor, start with that. Otherwise you'll need a scanner to view live data and see which signal is missing when you try to start the engine. Also check if you're missing spark or fuel pressure when it doesn't start.

Testing the ignition control module is useless and won't tell you anything when the problem is intermittent. The fact that the engine runs at all tells you the module works at times, and not at others. You have no way of knowing if it's in its good state or bad state when it's being tested. The testing has to be done when you know the problem is occurring, and that testing will have to be done on the truck. If you have a total failure and the engine never starts, THEN off-vehicle testing might identify a defective part.