325ix running rough on start up - revving fixes issue

[D.Martijn]

What is your charging voltage at idle?

I'd have to check. I did rebuild the alternator roughly a year ago. Installed a new rotor as well and voltage reg.

Check ohms on coolant sensor, and make sure the TPS is reading idle switch. If one/both are bad, you will run excessively rich on idle and low part throttle maps.

I replaced both sensors with new one.
There was a 400ohm difference between the old and new one.
Yeah that's next on the list!

[D.Martijn]

A friend of mine tried reading the ECU it's fault codes but somehow couldn't get a connection with his computer, which on this E30 worked just fine.
Last evening I started the E30 again and with the ICV connector barely connected the idle raised, I was able to repeat this a couple times but after a while I couldn't get it to do this again.. Some bad connection some where? bad engine loom..?

So I followed this trouble shooting guide from RTS auto, and everything seems to check out. Also the resistance of 40ohms to the ICV. As well as the TPS on idle is continuity and WOT too, nothing in between
https://www.rtsauto.com/ecu-pinout-a...cal-tests-e30/

[laidback93]

I had/have this same issue with my 325is. I did everything you have done. Smoke test (no leaks), new ICV, new TPS, coolant sensors, swapped AFMs and DMEs. Also replaced the FPR and fuel pump. I too had a very bad rich on cold start issue. To the point you would smell raw gas from the exhaust.

Flash forward to a couple weeks ago and she is running much better, not perfect from the factory, but much improved.

So here’s what helped. The C191 plug was heavily corroded. It was replaced with factory connectors. My fuel injectors were leaking pretty bad so they were replaced with new OEM. I also went back to a stock flywheel when I had the clutch redone. The PO installed a 7lb JB Racing flywheel which was just too aggressive for my E30 which I daily. And finally the kicker… turns out the fuel pump installed last year was defective. The check valve came apart. No more long ass cranks on cold start up.

Here’s the crazy part. My mechanic did a compression check when I had the clutch job done and all 6 cylinders have very low compression. Like 115-120 range. It’s hard to believe as my M20 runs very strong all the way through the power band. It doesn’t smoke or is mixing coolant and oil. He thinks this is why I still have a slight stumble off cold idle and our very warm weather is masking the problem. This would make sense at this idle issue is the worst when it’s cold outside.

Sorry for the long winded post. I could write a book about the history I have with my E30.

have you made any progress or discoveries on your E30!

[D.Martijn]

I actually was able to solve it.

A friend of mine told me to check compression, got 10-11bar on all cylinders. O that wasn't the problem.
However the last few time I tried starting the car I noticed the new fuel pump getting quite loud.
I figured it might be a good idea to replace the fuel filter because why not.. it's been 5 year or so (however I do have a new tank fitted).

Well it's been idling fine when I first started it after replacing the filter!