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Extremely rough idle when cold

Posted by Earendil 
May 10, 2010 08:27PM
I'm experiencing an idle when the engine is cold that is akin to have two spark plugs pulled. It's rough, and varies such that when the accelerator pedal is partially depressed, the car almost bucks.
It reminds me a bit of the time when I was a kid and while washing dad's car, decided to be extra helpful and wash his engine by taking a hose and spraying it for 5 minutes grinning smiley

My immediate thought is that it feels electrical, except that it goes away as soon as the engine temp is past the blue mark. I've tested the coolant temp sensor and it is fine. So what else is temperature sensitive and could be causing that much engine choking? I always thought the temp sensor was the only thing...

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

May 10, 2010 09:11PM
You know there's 2 temp sensors- 1 for the dash and the other for the Motronic? Maybe the Motronic one is stuffed...

Other possibilities are the Idle Control Valve and the engine earth (maybe there's moisture that goes away once the engine bay gets nice and warm).

Hope this helps,
Simon
May 10, 2010 09:18PM
Quote
Earendil
I'm experiencing an idle when the engine is cold that is akin to have two spark plugs pulled. It's rough, and varies such that when the accelerator pedal is partially depressed, the car almost bucks.
It reminds me a bit of the time when I was a kid and while washing dad's car, decided to be extra helpful and wash his engine by taking a hose and spraying it for 5 minutes grinning smiley

My immediate thought is that it feels electrical, except that it goes away as soon as the engine temp is past the blue mark. I've tested the coolant temp sensor and it is fine. So what else is temperature sensitive and could be causing that much engine choking? I always thought the temp sensor was the only thing...

Have you tried pulling the Motronic codes to see what the issue is?
May 10, 2010 09:30PM
Quote
Archeo-peteriX
Have you tried pulling the Motronic codes to see what the issue is?

(off-topic) I am sooo jealous of your American-spec cars being able to do the "stomp test" to read the codes! It's not fair, wish I could do that!
May 10, 2010 10:05PM
Quote
nomis3613
You know there's 2 temp sensors- 1 for the dash and the other for the Motronic? Maybe the Motronic one is stuffed...

Other possibilities are the Idle Control Valve and the engine earth (maybe there's moisture that goes away once the engine bay gets nice and warm).

Hope this helps,
Simon

Really? I was only aware of one... But I follow the Bentley, so I'm assuming that the one I know about, the one on the thermostat housing, is the one for the ECU.
I didn't know the idle control valve had anything to do with temperature? And wouldn't the ICV become a non issue once the throttle is no longer closed?

Moisture had occurred to me, but this has been happening on the last 6 or so starts over 3 days. 3 morning starts, 3 afternoon starts (when it was warm and sunny).

Quote
archeo
Have you tried pulling the Motronic codes to see what the issue is?

The only code is 1221 O2 Sensor out of whack. It comes on every so often for seemingly no reason. But only once every 4 or 5 driving hours, and never in the morning. I replaced the O2 sensor last month becomes it was being set off every 5 minutes, even though the engine was running better than it is now.

Quote
nomis3613
(off-topic) I am sooo jealous of your American-spec cars being able to do the "stomp test" to read the codes! It's not fair, wish I could do that!

It is quite nice, if only for ease of mind. The Check engine light goes off, and it's helpful to be able to pull over, check and see that it's an O2 sensor code, and hop right back on the freeway without worrying that your engine will blow. However I often wish it gave MORE info smiling smiley

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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