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DISCUSSION => Engine + Driveline => Topic started by: deansweet on February 26, 2012, 07:16:26 PM

Title: Weird idle Issue when warm?
Post by: deansweet on February 26, 2012, 07:16:26 PM

Well, it's weird to me?
1991 E30 M42. All Stock.
When the car is initially started the idle does as it should with a steady above normal idle until it gets warm. Once at normal operating temperatures it tends to stumble at idle? Cyles up and down. It seems to be running just fine otherwise and getting normal MPG's.

I have checked for vacuum leaks and found none.
All vacuum and coolant lines are still under the intake.
Plugs look good for being somewhat brand new.
Any other suggestions?

Thanks
Dean

Title: Weird idle Issue when warm?
Post by: Wrench on February 26, 2012, 08:43:52 PM

Hey Dean, that's my name too. :)
I would suspect the O2 sensor, or an air leak somewhere.

Title: Weird idle Issue when warm?
Post by: Got Mayhem? on February 26, 2012, 08:44:41 PM

Could be the catalytic converter plug. Against the fire wall in the engine bay there should be a collection of wires, they might be under a case. All the wires should be bundled together except one, a single male-female white plug. For 318's with a catalytic converter it should be unplugged and vice versa.

There's a sticky at the top of this sub-forum about it with a diagram but it's very easy to find.

Title: Weird idle Issue when warm?
Post by: DesktopDave on February 26, 2012, 10:03:02 PM

I'd figure O2 sensor, coolant temp sensor or intake air temp sensor.

Title: Weird idle Issue when warm?
Post by: asmir on February 27, 2012, 05:34:17 PM

Check wires for oil sensor and coolant sensor.Happened to switch this two connectors

Title: Weird idle Issue when warm?
Post by: deansweet on February 27, 2012, 08:01:29 PM

I labeled the sensor plugs on upper intake side of head when I replaced them so I seriously doubt I plugged them in backwards but I will pull and re-seat them just in case.

Is the air intake sensor right at the air filter housing? That thing rolled off the roof of my car when I was working on it and cracked where that plug is on side of AFM? I guess that could be the problem...

Title: Weird idle Issue when warm?
Post by: DesktopDave on February 27, 2012, 09:17:53 PM

The air sensor is pins 4 & 5 on the AFM IIRC.  Lemme dig up that thread...

According to the 3 series repair manual:

Intake air temp sensor @68degF 2200-2700 ohms; at 122degF 760-910 ohms.
Coolant temp sensor is very similar: @58degF 2300-2700 ohms; at 180degF 300-360 ohms.

Title: Weird idle Issue when warm?
Post by: deansweet on February 28, 2012, 07:00:35 AM

Anybody got a spare AFM they want to sell? :)

Thanks Dave.

Title: Weird idle Issue when warm?
Post by: deansweet on March 01, 2012, 10:12:57 PM

(https://lh5.googleusercontent.com/-0vluavAlDqI/T1APCPIACqI/AAAAAAAAAsk/kEmC4yJIOGg/s800/IMAG0624.jpg)

All this for $70
AFM, Bosch Premium Alt, Idle Control, Intake tube with no cracks!