I have a 1991 GMC s15 jimmy 4x4 with the 4.3L 'Z' engine. It has 197K miles and has been in the family since new. A couple of weeks ago, the idle started to run very high and the "service engine soon" light came on. The truck also became very hard or impossible to start when cold, but starts okay even if it has only been sitting in the sun for a couple of hours and isn't at operating temp.
Many parts have been previously replaced for preventive maintenance, including:
- Everything electrical/mechanical on the throttle body injection, including new injectors, throttle position sensor, idle air control.
- All ignition parts are upgraded quality and in new condition.
- Just replaced the gas tank, fuel pump, sender, and fuel filter. (The old pump had failed but the replacement didn't make the vehicle run any better than it had been.)
I asking here because I'm out of ideas. Could a plugged catalytic converter do this? (It's still on the original one.) There's no ODB port to connect to or anything, so I'm stuck with old-school troubleshooting.
Any thoughts? Many thanks in advance.
-Jonathan Ward