Rough idle and occasional 1271 code - until engine warms up

[dmaj]

Hello all,

My 318is recently developed a rough idle problem at start up (cold). Occasionally throws a 1271 code (ignition problem). Once the car starts to warm up, however, it idles and drives fine. Compression test looks ok but it's a high mileage engine due for a rebuild and there's a bit of oil on two of the spark plugs (electrode side). I don't understand why the car would have an ignition problem, either with the coils or wires, but run fine once the engine is warm. Any thoughts?

[roguetoaster]

Maybe start by testing the crank and cam sensors. It could also be the start of a coil driver failure at the DME.

How is it operating at high RPM? Any issues with a hot restart?

[dmaj]

No issues at high rpm, nor with a hot restart. Only when the engine is fully cool will it act up.

I'll take a look at the sensors - thanks. Worth swapping DMEs with a known good one to check it or is there a test I can perform?

[roguetoaster]

Might be worth swapping in another DME just to check.

While you have the multimeter out it's worth checking the wires and coils when, doubtful it's the issue, but it's a n easy check.

[dmaj]

Found a bit of corrosion on the plug wire for cylinder one. Cleaned that out, let the car sit overnight, and it fired right up in the morning. Just the slightest hesitation at first but none of the rough idle (and occasionally misfire - I forgot to mention that) I was experiencing before.

That's all well and good - but any thoughts as to why the engine would seem settle into a happy idle with good power after 3-5 minutes of warming up? This wasn't a gradual transition but rather a distinct switch from running poorly to perfectly. Could this be a function of the time it takes for the DME to figure out how to run the car reasonably well with an ignition problem? (This is the part where I don't really know what I'm talking about...)

Thanks again for the help thus far.

[roguetoaster]

Found a bit of corrosion on the plug wire for cylinder one. Cleaned that out, let the car sit overnight, and it fired right up in the morning. Just the slightest hesitation at first but none of the rough idle (and occasionally misfire - I forgot to mention that) I was experiencing before.

That's all well and good - but any thoughts as to why the engine would seem settle into a happy idle with good power after 3-5 minutes of warming up? This wasn't a gradual transition but rather a distinct switch from running poorly to perfectly. Could this be a function of the time it takes for the DME to figure out how to run the car reasonably well with an ignition problem? (This is the part where I don't really know what I'm talking about...)

Thanks again for the help thus far.

My guess would be that when cold the car may spray more fuel, and with a weak spark you get poor combustion. As the mix leans out it would run better.

[dlmrun2002]

nice

My guess would be that when cold the car may spray more fuel, and with a weak spark you get poor combustion. As the mix leans out it would run better.

I like your thinking. I should start my 318is......................someday
dlm ny country

[dmaj]

Well that seems like a pretty reasonable explanation. I like it. Car runs like a champ, now. Pretty easy problem / solution - I suppose I was just thrown off by how well the car seemed to run when warm. Thanks again.