I have a 1990 Chevy S-10 Auto with a 4.3 V6 it has a rough idle when its stopped in gear. Ive tried everything tune up, sensors, timing, ect. nothing works. It has descent power and just driving it seems fine but when you come to a stop light it runs real rough. It almost seems like something is out of balance. It has a lockup converter so I don't know if that has anything to do with it but it seems to work ok. I'm out of options anyone else have this kind of problem with a 4.3?
Chevy 4.3 rough idle that no one can figure out.
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4.3s shook a little bit at idle up until they started building them with a balance shaft.... which they didn't have until 1992.
I had a S-10 that had a miss at idle,, slight but you can hear/feel it, the problem was the cap that was put on,, it was new and a good one, Conrad from AZ,, put on a GM cap and the truck still purrss like a cat today,, also check the base gasket of the TBI unit, I would remove and clean the TBI unit with throttle body cleaner,, if it has never been removed for cleaning that could help,, I have seen the bottom of some TBI units so gummed up it did not have enough vacuum to work the PCV valve,, matty man 8)
sounds like limp home mode. If a tbi vehicle goes into it b/c of a bad sensor it wont come out till computer is reset. Try unplugging the battery. takes two seconds and if it doesn't work it wont cost anything.
Are you talking about the ignition module itself, or the pickup coil? I've had two pickup coils go out on a previous truck (350 TBI) and it wouldn't run at all.
I've never heard of limp-home on a TBI, closest thing I can think of would be it going into open loop, and it runs on a set safe-run table, but that shouldn't make it shake like it does.shadychevyowner said:
I had a 1992 GMC Safari van with the 4.3 that usually ran great, but at a slow idle, it started to shake a bit. Turned out that a vacuum hose came off that was located near one manifold runner. Re-attached the hose and it ran great again.
On those older 8 bit ECMs, if a sensor goes bad, and the ECM flags it as bad, it will not use the sensor, but substitute a value for the bad sensor. This is not limp home mode. Limp home is where the PROM has a bad checksum, or some other processor malfunction that will not let it properly run the program. There is a hardware based backup fuel mode that takes over that will let the engine still run, but at a very rudimenary level with no ECM calculations. That is the limp home mode.
The fuel calculations are the same and use the same code and tables in closed loop as in open loop, there is just no active fuel correction in open loop.
On those older 8 bit ECMs, if a sensor goes bad, and the ECM flags it as bad, it will not use the sensor, but substitute a value for the bad sensor. This is not limp home mode. Limp home is where the PROM has a bad checksum, or some other processor malfunction that will not let it properly run the program. There is a hardware based backup fuel mode that takes over that will let the engine still run, but at a very rudimenary level with no ECM calculations. That is the limp home mode.
The fuel calculations are the same and use the same code and tables in closed loop as in open loop, there is just no active fuel correction in open loop.
You did a better job explaining what I was thinking... guess I was a little wrong in my explanation 
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