Rough Start/Idle, Power loss under acceleration (Code 1223)

[318isguy]

Hey I'm a newbie to this forum and looking for some help.

On my way to school today came to a stop at a stop sign and my car stalled randomly. Took me a few tries of turning off my car and on again for it to turn over, and when it did it had a super rough idle. I turned it off again, waited around 30 seconds then started it back up and my idle sat around 1200. When I press the gas pedal I would get power loss and my engine would almost die. I ended up parking it at school for a few hours and got it running after a few minutes before heading home. I stomp checked my engine light code at home and it threw the code 1223 for my coolant temp sensor but I was wondering if anyone would have any other ideas of what this could be? I've read online that the c191 connector on m20's was a big problem but can't find anything on it or like it for the m42.

Any help would be appreciated, thanks

[monty23psk]

Could be a few things. The fact that you have an error code I would address it as it will affect how the engine runs. I would suggest clearing the codes and then see if the problem returns or after a few drives, do the stomp test and see if the same error code appears. If it does, replace it/reset code and see if it happens again. Did the check engine light turn on?

[bmwman91]

A bad coolant temp sensor can definitely cause big issues. Sometimes it is the sensor itself, sometimes the wire fatigues and breaks in the plug, so get in there, pull the connector boot back and see it is intact.

[318isguy]

Replaced the blue temp sensor under the intake and all the wires seemed to be in good shape for their age. Still have to remove the cel to see if it solved my problem. Will most likely remove the intake manifold and replace the black sensor (the one inaccessible without intake removal) as well later this week. I've read that to clear the cel you can stomp test, wait for your code to flash, then hold the gas pedal down for 15 seconds to clear?

[monty23psk]

I have never heard of resetting it via the stomp test, only unplugging the battery or have the computer to reset. Worth a shot and do a web search if not working.

[DesktopDave]

I'd toss a DMM on those sensors to see if they're good or not. They're an negative temp coeff. (NTC), so you'll see high resistance at lower temperatures. Resistance will fall off as temperature climbs. There's another one integrated into the AFM for air temp that's easy enough to check while you're in there.

I'm sure you won't make any mistakes like i did, but if you pull the intake I have some advice:
Be prepared to do some serious cleaning, the E30 lower manifold is especially fond of caked-on oil residue.
Get extra manifold gaskets just in case. I like to prep the paper ones with non-hardening sealant.
Consider doing the oil filter housing o-ring & gasket.
New injector o-rings are also a good idea, and they're cheap.
Don't touch the plastic cooling manifold unless you have an OEM BMW part to replace it. They will crack if you even look at them the wrong way. Consider doing the hose delete (E30 only) if you haven't done it already.
I'd also mark all the two-pin wiring plugs.

I almost cracked my lower manifold because I had installed it wrong. It hung up on a locating dowel in the head. Had I fully torqued it before I caught my mistake, I'd have cracked the mounting flange. The plugs are incredibly easy to mix up since they use the same two-pin EV1 connector, and cause all sorts of fun if you get them wrong. Say you mix up a temp sensor with the oil pressure sender...the car will suddenly run rather badly...perhaps making you think you've left the manifold loose...then you might rip a gasket when you take it all apart the 2nd time...experience is a harsh mistress...

Also, no matter what happens to an M42, I check the crank position sender. Nervous habit, I suppose. You should see about 1Kohms or so. CPS are notorious for causing rough running & no-start problems, and don't set a code at all.