wtf is wrong with my m42

[bmwm42]

Issue started a few days ago......car starts fine...idles fine.....but when I hit the gas car falls on its ass unless I get above 3k rpms......issue started happening only within the first two min at cold start up.......now its just getting worse.....so far ive ruled out fpr cam sensor temp sensor afm......wtf can it please help

[roguetoaster]

I am guessing no codes or you would've specified. How did you rule out the components, multimeter tests? If so I would suggest unplugging one component at a time until the situation no longer exists. Otherwise you have the magic invisible vac leak that only gets going when something expands.

[bmwm42]

I replaced them from my spare engine that is perfect.....no codes....car back fires if I try to hit the gas to soon.....I have a cop kit.....tomorrow ill try a new ecu....I'm lost.....car just stalls and is getting progressivly worse every day

[roguetoaster]

Backfires you say, hmm. Sounds like the crapcan 318 I had for a bit, turned out to be the AFM had water in the case. You wouldn't happen to have the resistor in line in the AFM wire, you know the one that uses two of those round connectors?

[bmwm42]

Nope no extension in place.....this engine was running beautiful....then one morning as I go to hit on the gas it falls flat and stumbles and then everything goes back to normal.....spark plugs aren't fouled....wtf

[roguetoaster]

I think you may very well have a vac line that has come slightly loose.

When it stumbles off idle and you give it more throttle, does it dip below idle for a moment and then pick right back up?

EDIT: for another random one, I had a car that had the O2 sensor come loose, as in backing out of most of it's threads, did a similar thing. Also managed to get the same issue after tightening the sensor back down only to forget to plug it back in. Clearly wouldn't happen off of a cold start, but there you go.

[bmwm42]

Checked all vac lines no mess under intake all hoses new ill have to check the oxy sensor

[duleymane///iS]

http://www.m42club.com/forum/index.php?topic=7757.0

Have you tried this? Sounds exactly what it is if you haven't tried it. Pull the cover off the wiring harness inside your engine bay. There is a wire that is all by it's self and is outside of the loom, unplug it. I believe it bypasses the O2 sensor completely. Mine is unplugged as well as my O2 sensor, car runs great as soon as I plug in that mystery wire the car does what yours is doing falls flat on its face. Hope this helps...
or here.

http://www.e30tech.com/forum/showthread.php?t=105848

[bmwm42]

Update swapped ecus still the Same unplugged oxy sensor no change....I'm stumped car back fires at low rpms

[wazzu70]

Sounds like an AFM to me. Did you test your current one?

[bmwm42]

Yup have several spares I tried the car without the afm connected and still no change......I dont have a crank sensor to swap maybe that's the issue

[wazzu70]

Have you checked the TPS? ECU coolant temp sensor?

[bmwm42]

Yup they check out......at this point I'm going to do a vac test and also check my coils and see if I don't have a dying weak coil

[roguetoaster]

I am sure it will be simple and obvious when you do finally find the solution. In case you need to know, the coils should be between .4 & .8 ohm, and the plug wires between 4500 and 5500 ohms.

[duleymane///iS]

Any fuel issues? like a leaky injector dumping in too much fuel? I might(probably) am completly wrong but it could be putting in too much/not getting enough fuel? clogged fuel filter?