I have an 87 325is. Randomly the idle will go up and down then it throws a check engine light. rev it a little and its back to normal. Idk what it is. ICV? But also some times while driving at a constant rpm usuallu 4k or just above the check engine light comes on but it drives fine.. nothin changes but the light and when you rev it it goes off, but sometimes.. when i push in the clutch and let it drop to idle it goes up and down.. then rev it once and it quits. Idk im confused? And some days starts up normally and never had any issues.
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I had a very similar if not that exact problem. Turned out to be either a big leak in my intake on the big rubber elbow or the O2 sensor which I fixed/replaced both at the same time.Comment
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Your intake elbow was leaking? How can i tell if mine is? And Also i might try o2 sensor first if i can find one fairly cheap. Thanks for your inputComment
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sweet so what do you suggest i do?Comment
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check your connections for proper fitment to start with. that's as far as i needed to go.Comment
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ok will do. Otherwise for the o2?Comment
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ok YOu think that could cause this?Comment
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think i read it somewhere on here. i'm not a pro. just sharing what worked for me in the past.Comment
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ok man thanks ill buy one and switch it outComment
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I had this issue with mine last week. Recently I had done a new 02 sensor, plugs and wires, and my old plugs were white as hell (super lean issue). The 3 ports on the side of my throttle body were somewhat loose, and they were causing an vacuum leak. Once I had sealed up the rest of the engine, it was running funky and threw a CEL...once I epoxied the fittings back into the intake and cleaned out the intake boot ( i thought it was torn but it was good) and changed the air filter (was clogged like you wouldnt believe), she smoothed out and runs good as new again.
Check for vacuum leaks...its most likely the culprit. Even worn o-rings on the dipstick can cause this issue...Comment
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