'93 Rangie, 4.2. Beautiful shape, but when it warms up, the idle begins to hunt, the Rovacom shows it going rich, then eventually, it dies.

Sensors all appear well. I disconnected the purge canister solenoid thinking it might be causing the enrichment, it helped a little, but then, it does it again.

It's hard to start once this happens until it is allowed to cool, then it's fine. Seems to run well, except at idle-dies at stoplights.

Any ideas? Really perplexed on this end.

Peace,
PT

Substitute a known good ECU for testing.

I know you got one.

JP

what is the fuel pressure at?

Also worth setting the base idle/messing with the air bypass valve.

Ghost in the machine.

Bad O2. I have seen this at least twice.

same thing happened on my rig- was a combo of bad Ignition amp module and 02.

Thanx fellas-even you Pendy :flipoff2:

For some reason, I never look at the ECU as being a source of such problems and most likely, they are the source.

I will swap a known good ECU-if this doesn't do the trick, I'll throw in a set of O2 sensors and maybe an ignition amp (it won't be a Lucas :D )

Peace,
PT

i have a similar issue - let me know the outcome. I keep forgetting about the ignition amplifier. have new o2's, and lots of new everything else. truck runs great until it warms up, then starts hunting for the idle and running rough just as you describe.

hmmm ... where was that gm thread ...

speaking of GM amps - are there long term success stories for this conversion?

Now I'm beginning to wonder if it is the ignition amp and the rich condition is a result of the unburned fuel from the lack of spark.

Maybe I'll swap that first.

Just as it looks like I'll get Shopgrrl's truck going (thanx a lot Pendy) and this shows up and he's family too.

I ASSUME that the Rovacom "rich" reading comes from the oxygen sensors. Have a sniff of the exhaust. Is it really rich or not? You should be able to tell from a smell. If not, the sensors are probably the problem. If not, it be somewhere else. But hey, what do I know about these new fangled contraptions.

This summer my truck started doing the same thing. Hunting for a stable idle. If I reved it up in park, it would drop down below normal idle rpm and die. NO codes. So I Took out stepper. It looks fine But clean it anyway. Truck does have charcol black tail pipe and emits a little black smoke. I have been following related post for sometime and holding off on new o2 sen. Over the weekend I spray contact cleaner to all sensor multiplugs on maf/o2/step etc. When I got to the forward drivers side o2 I felt a wear spot underside of the wire sheath. The white wire was bare and sitting on the bell housing un visible from above. I wrapped in elect tape and the car doesnt bobble anymore. JP