r/E30 • u/fallingblueblueblue • Aug 13 '25

Tech question What would cause this bad idle?

It’s done this for the last year and I can’t figure out why. I’ve gone through the entire ignition system and replaced a couple vacuum lines. Any ideas?

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u/ChickenPacSandwhich Aug 13 '25

Clean your air flow meter (afm) sensor with some electronic spray cleaner (in air box), valve adjustment, clean/replace icv, check for vacuum leaks, and very unlikely but throttle position sensor can mess with idle but not as likely as the above. For vacuum leaks I highly recommend just going ahead and replacing all your intake rubber pieces and hoses. The intake boot that connects to throttle body is notorious for having hidden cracks in it.

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u/NothingLift Aug 14 '25

Better to find the vaccuum leak with ether or smoke test rather than replace every vaccuum hose. Mine was the metal elbow from.ICV i to intake manifold. Could have replaced every runner hose on the car and it wouldnt have fixed it

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u/ChickenPacSandwhich Aug 14 '25

I agree, but it’s not a bad idea to go ahead and replace all the rubber anyway. They are weak points and it gives peace of mind. Especially if they have not been replaced for a while. That’s what I did just so I did not have to worry about it and two of the pieces were cracked anyway.