M20 will not cold start with AFM plugged in (runs good though)

[Zardog]

I have a 87' 327i with a 731 head. The engine runs good but it will not start cold with the AFM plugged in! I can unplug it and it fires right up. Usually, then I can plug the AFM back in and it will run a little rough but it smooths out pretty quickly. The car has a Motronic 1.3 swap and it has a chip in it but I am not sure what chip it is (installed by PO of stroker parts) I purchased the 1.3 setup from someone with an identical setup with only one difference. He ran a 325i downpipe and I still have an ETA one. My hypothesis is that it may be flooding on startup because it cranks and cranks with a few sputters. When I start and but AFM back the Idle rpm is quite low for a cold engine (~900).

Anyone know if the downpipe could be a cause of a rich running start or should I invest in a new chip for the ECU? Any other ideas? Bad AFM maybe? Thanks!

[ForcedFirebird]

M1.3 requires the blue temp sensor on the thermostat housing. If the PO forgot to swap it when changing the DME, then the readings are all wonky. If you have the blue sensor, verify the ohms, want to say it's 320 at operating temp (from memory, please check).

Next is the TPS, believe it or not. If the TPS idle switch is malfunctioning, then the DME "thinks" your foot is slightly on the throttle, even though the throttle plate is closed - therefore adding fuel to compensate the open throttle (causing rich).

EDIT: I have seen 24v swaps running ok through eta single exhausts on customer cars at work, no way the single/smaller down pipes are causing a major daily-driving issue (might be down a couple hp).

[traciegrier]

Many thanks for that.

[Gregs///M]

Its nearly impossible to find any 30+ year old AFM that still works decent, with that said, your AFM is most likely failed. I have seen cars that are perfectly running fine and gain significant amount of HP when swapping to a rebuilt AFM. It can also improve idle quality, horsepower and torque and help with smog. Anyone that is trying to restore their AFM and have their motor running well should have a refurbished AFM.

[Zardog]

I replaced the tps and blue temp sensor at the same time which pretty much resolved the issue. The tps was junk, but the blue temp sensor resistance was fine when warm but off when cold. I previously only tested it after warmup. Also my afm clock spring was messed with. It was 6 teeth counterclockwise, but luckily whoever moved it marked original location. I rolled it back clockwise a few steps and the car seems much healthier and doesn’t backfire between shifts. Thank you ForcedFirebird! Edit: (forgot to mention I took apart my afm and cleaned it. Then I adjusted it so the swing arm rides on a new part of the contact patch not the groove part. A little brake clean and scotch brite on the outside and it’s good as new. No need to pay 300$ for a fancy “refurbish” that is basically just a disassemble and clean” )