Rough Idle, can't hold rpms

[e30sh]

Fuel pressure is a little low. Could be cheap gauge / weak pump / semi clogged fuel filter.

Have you checked the the blue top temp sensor...it sends a temperature signal to the DME to adjust mixture based on coolant temp.

Have you done a compression test to confirm the engine is mechanically sound?

How do the plugs look?

[Sladek]

it is a pretty cheap gauge but I ordered a fuel filter since it could probably used replaced. haven't done a compression test but before I did this work it was very sound. what's the blue top temp sensor?

maybe I need to clean/replace the afm? it runs worse when I unplug it

[e30sh]

what's the blue top temp sensor?

In head right above block cylinder 1 drivers side. Unplug, check resistance of sensor hot and cold.

See if your plugs are gas / oil fouled / gaps / wrong kind etc.

[Sladek]

how would I test that it's good? I tried going through each cylinder unplugging the spark plug wires and the engine didn't run and worse with any of them unplugged. all the spark plugs are new and gapped properly

[e30sh]

Resistance output changes with coolant temp. Set your meter to ohms. Don't remember the exact values but it's listed in the Bentley manual.

You could pull your current plugs just to get an idea of mixture.

Do you have anymore plug wires? I had a cold skip (not as bad as yours) a few years back in a M42. Turned out to be a plug wire.

[squidmaster]

You have a multimeter I assume then? Test the AFM output. Manually move the barn door and watch to see that it's a gradual resistance change from closed to open
pretty good information on it here: http://www.unofficialbmw.com/e30/ele...t_testing.html

But, if it's much worse with it unplugged, the problem could lie elsewhere.

Unplugging one wire on an M42 should make a bigger difference than "nothing", so that's odd

[Sladek]

I've got a multimeter I'll try a few things tomorrow and see what I can come up with

[Sladek]

is the plug to the left of the valve cover supposed to be plugged into something? I was looking at O2 sensors and it looks like a similar plug (I'm not at home so don't have a close picture)

[e30sh]

Is the plug to the left of the valve cover supposed to be plugged into something? I was looking at O2 sensors and it looks like a similar plug (I'm not at home so don't have a close picture)

That is the O2 harness. The O2 sensor lead from the exhaust is "normally" on a plastic hanger clipped under the battery tray.

[Sladek]

That is the O2 harness. The O2 sensor lead from the exhaust is "normally" on a plastic hanger clipped under the battery tray.

so dumb question of the day, does that mean it should be plugged into the o2 sensor from the exhaust? I haven't messed with anything on the exhaust but the previous owner cut out the cat, not sure if that means he somehow got rid of/unplugged the o2 sensor. my battery is also in the trunk

[Sladek]

and if it is supposed to be plugged in shouldn't it have thrown a code?

[Sladek]

I also checked all the coil wires and each of them made the engine very angry upon unplugging a cylinder so I assume that rules them out since they are working and my spark plugs are new

[squidmaster]

Stock injectors? Does it have a tune? Is the o2 sensor still in the exhaust? Can you wire it back in?

[Sladek]

Stock injectors? Does it have a tune? Is the o2 sensor still in the exhaust? Can you wire it back in?

I've tried both stock and new mustang injectors. it's got a dinan chip.

haven't had time to check and see if the o2 sensor even exists (from the sound of it, it's supposed to be plugged into that empty plug in the engine bay?) like I said I know the previous owner cut the cat out and just had a pipe welded in. car has been on the ground for a while and I didn't even think to check and see if the o2 sensor was gone too. I would've thought it wouldn't even run at that point

[e30sh]

The O2 sensor bung is pre cat so it should still have a spot in the exhaust unless someone cut out more than normal. Plug it back in and report back.