M42 erratic running on startup

[GT Technic]

I have two older cars with M42 engines which peculiarly suffer the same issue. On first time startup in which the engine starts normally, the engine can't exceed 1,000 rpm. It's as if it is being rpm limited. After about a minute it can reach about 1,500 rpm and after about 2 minutes, it runs as it should. This is not an intermittent problem. It happens all the time. It is more severe in the colder weather in terms of time before it runs normally. I'm thinking this is a computer issue, but I have changed computers and the issue stays the same.

Then after going to the store and restarting the engine, it runs erratically for about 30 seconds before you can give it full throttle and be able to move away from your parking spot. If you try to move right away, the engine will bog down, so I have to clutch in and blip the throttle which will make the engine cough and sputter with the occasional backfire. In this situation to my mind it's clearly running rich.

I have changed the temperature sensor under the manifold without effect. I believe from memory the sensor toward the front is more for the gauge which works correctly but has also been changed.

Has anyone experienced these issues that could share their experience?

[shogun]

Moved from Forum Software Questions & Suggestions to E36 forum

[Eric93se]

If you have the vane style MAFS then this might be your problem. They sell them rebuilt usually and they're not cheap so maybe just get one.

You should put the year and model too when asking for help.

[GT Technic]

Thanks for the suggestion. I think I swapped mine out for another early on, and the problem persisted, but I'll try this again. I've lived with this problem for almost two years and other than the computer and a faulty temp sensor, there's nowhere else to go since it runs like a champ when it's warm.

[Eric93se]

Well I would suggest doing tune up items. Smoke test the engine for vacuum leaks. Spark plugs, pre-cat oxygen sensor, ignition coils, use injector cleaner over the next 3 tanks of gas (I like royal purple). Test your crank sensor (510 ohms).

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Not sure if the engine ground strap is like the straight six, but remove it and wire brush all contact surfaces and spray clean liberally with brake cleaner (low VOC) or contact cleaner.