Unsteady idle, O2, '91 Trooper

  • 1991 ISUZU

1991 2.6L 4ZE1 4 cyl. Isuzu Trooper; 120,000.
In neutral, on a cold start the idle is particularly rough, still problems with a warm start but not quite as bad. On cold, the idle goes to about 1200rpm then down, feels/sounds like gagging and almost stalls, rpms way low like 300 (has actually stalled out sometimes). Then jumps up to 1500 where it stays for a bit, then unsteady, and then drops some to around 1000rpm, sometimes sits lower like around 800. Remains unsteady. When warmed up fluctuates between 800 and 900, sometimes 1000rpm. There also appears to be sort of a clacking, ch-ch-ch-ch sound in the engine area that has unsteady rhythm kind of like the idle, and I may only hear this now because the former exhaust leaks are not drowning it out, but not sure.

Looking though some other posts and replies, might any of the idle air control (IAC) valve, EGR valve sticking open, vacuum leak, and fuel injector leak suggestions apply here? I don’t know how to check any of this myself or know if it’s possible outside a shop (note last paragraph).

Had it in the shop recently after changing oil, filter, and new air filter myself and asked them to look things over seeing as 120,000 is major tune-up time – gave them notes I had on each of the most recently replaced components or repairs in the 120,000-mile user’s manual list. General check over (not sure it was so thorough, though), replaced catalytic converter (rust hole in last one), manifold gasket, power steering flushed and leak worked on, throttle housing cleaned, and “foreign object” removed from flared joint between EGR pipe and exhaust manifold that was causing a leak by not letting the male and female ends sit together. None of this has helped the idle, although getting the exhaust fully enclosed allows one to hear the engine noises much better.

Asked them about the 02 sensor light because it’s not been turning on during the “bulb check” during start-up, but they said if there were problems with the O2 sensor itself, the “check engine” light should come on and that I’m better off not having the O2 sensor light coming on at the preset 120,000 and staying on until it’s replaced. Is this the case or should I really get it replaced now? (Was formerly replaced at 90,000 in ’96 before the car was given to me in 2002 after sitting for like 5 years – went through degree of overhaul before road ready). I am planning to at least figure out why the bulb isn’t doing its start-up “check” – instrument cluster off to access? I don’t think the switch “behind the speedometer” that was mentioned in some other posts could have been bumped, but still trying to locate that too.

Had a lot more questions for the mechanics, but being a girl they didn’t seem to take me seriously. I have learned a lot from this car in 4 years and plenty of issues to deal with – and want to learn more. I have had the Haynes manual from the start and read it thoroughly every time and do my best to understand what is or might be going on and what is likely wrong before taking it to a shop. I think I’ll have to take some formal classes to earn any respect.

Thank you for any suggestions on anything/everything!

Do you
have the same problem?
Thursday, June 1st, 2006 AT 2:48 PM

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