M20b20 idle slightly hunting

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Onure30
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Fri Oct 10, 2025 3:52 pm

My e30 320i has a weird idle surging problem and when its warmed it runs super rich.

Ive checked everything and nothing has solved it.


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BenHar
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Fri Oct 10, 2025 6:52 pm

Try looking through the wiki.
There is a lot of information in there.

Ben
Speedtouch
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Sat Oct 11, 2025 1:57 pm

As above. Interesting to see the AFM in operation as you rev the engine!

I would carefully check all around the inlet manifold and intake area for air leaks - try spraying starting fluid around the various joints to see if the engine revs briefly rise, which would indicate a leak.

Also, which ECU do you have? Later Motronic 0 261 200 380/381 versions had extra diodes in the idle control circuit, which are prone to blowing, causing such issues.
///M aurice
ECU Upgrade EPROM Chips, £40 posted within the UK. Note these are not Zone chips.
viewtopic.php?f=6&t=279421
Onure30
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E30 Zone Newbie
Posts: 25
Joined: Fri Nov 19, 2021 4:22 pm

Sat Oct 11, 2025 7:46 pm

Just done a smoke test and i can see smoke coming from under and left side of throttle body, to me it seems like the tps, maybe the o ring. Tomorrow im going to have a better look.
Speedtouch
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Sat Oct 11, 2025 10:12 pm

Interesting. Did you use a proper smoke machine, or just a fag? ;)
///M aurice
ECU Upgrade EPROM Chips, £40 posted within the UK. Note these are not Zone chips.
viewtopic.php?f=6&t=279421
Onure30
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E30 Zone Newbie
Posts: 25
Joined: Fri Nov 19, 2021 4:22 pm

Sat Oct 11, 2025 11:06 pm

Speedtouch wrote:
Sat Oct 11, 2025 10:12 pm
Interesting. Did you use a proper smoke machine, or just a fag? ;)
Not a fag but a vape actually lol
Speedtouch
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Mon Oct 13, 2025 8:56 pm

Haha, good one - must remember that trick! :)
///M aurice
ECU Upgrade EPROM Chips, £40 posted within the UK. Note these are not Zone chips.
viewtopic.php?f=6&t=279421
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