I have a 1990 GMC Safari with 4.3L TBI engine. Engine runs/idles very rough, I have changed/subbed all emission parts including ECU. All vacuum lines and cylinder compression are good. Complete tune up and rebuilt TBI, nothing seems to fix the rough idle problem. Any suggestions will be appreciated.
These chopped off Chevy 350s weren't known for good idle even when running correctly. Any ECU codes at all? Have you checked your power brake booster for a vacuum leak? This sounds like a vacuum leak problem to me.
A rough idling 4.3 *could* be caused by nearly anything. Luckily, you've changed everything, so it can't be anything. That just leaves it to be a bad replacement part or a less than accurate compression test result, or?
I would suggest (even though it's not possible) that there is a wire misfire, a dist cap crossfire, a bent plug ground tab, a sticking valve or broken spring/retainer, low compression, vacuum leak at a hose or throttle body gasket, out of whack MAP sensor, weak coil, flaky ign module, etc...
How does the engine feel at full power or cruise conditions? At what RPM if any does it feel OK?
Toyota MDT in MO
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