1992 E36 325i - Rough idle at all times. Hesitates when cold.

Hi,

I've got an issue with erratic idle on my E36 325i Coupé Non-VANOS.



It's not really the classic 400-1000 rpm surge, it's just erratic, sounds as if cams are swapped.

Tried disconnecting O2 sensor. No go.
Tried disconnecting TPS sensor. No go.
Tried disconnecting water temperature sensor (blue). No go.
Tried disconnecting MAF. No go.
Tried disconnecting IAT sensor. No go.
Tried another ECU. No go.
Tried another MAF. No go.
Fitted new rubber boot. No go.

Haven't checked the ICV as it's not surging as much as just being erratic.

It idles poorly at all times, when cold it surges a bit from 7-800 rpm in "jumps", and the engine hesitates while driving. Seems "nervous" in its running. After approx. 4 miles, the hesitation disappears as fog to the sun (litterally from one second to another!), and all is well - except for the rough idle as told above.

If I start the engine when it's hot, and drive, the hesitation is not present. It's only when driving for the first few miles after a cold start in the morning.



SOLVED!!!!!! CPS was the culprit.

Try checking the color of the spark plugs if the engine is running lean or rich. Pictures would be good.

Do you have any cam chain noise? I wonder if the upper tensioner (between the intake- and exhaust cams) might cause this?

Originally Posted by granlund

Try checking the color of the spark plugs if the engine is running lean or rich. Pictures would be good.

Do you have any cam chain noise? I wonder if the upper tensioner (between the intake- and exhaust cams) might cause this?

They are very light brown. A bit lighter than a fresh-from-tab 10w/60. Uhmmm :-)

How long has it been since you changed the plugs and coils? It may just need a good tune up.

Steve

Originally Posted by BMR_LVR

How long has it been since you changed the plugs and coils? It may just need a good tune up.

Steve

Coils have done 50000 miles, plugs was changed today.

50,000 miles ago (80,000 km), did you replace the coil rubber boots too?

Originally Posted by granlund

50,000 miles ago (80,000 km), did you replace the coil rubber boots too?

Yeah, it was 6 brand new BOSCH complete with boots. Ground connections from valve cover to coils are also intact.

New CPS will arrive later today.

Good luck. I don't think that the problem is the CPS, but it would not hurt to have a new one as they can crap out on you at the worst of times.

Let us know if you find a solution to the problem.

Steve

CPS was the culprit. New CPS and voila :-)

Congrats. I was under the impression that a bad CPS basically caused the car to just not run at all. I learn something new everyday. Thanks for sharing the solution.

Steve

BTW, would you be kind enough to check the resistance on the failed CPS? I would be curious to know what the reading was. If it is in the normal range (540 ohms +/- 10%), then that makes the resistance check rather unreliable for establising the health of the CPS.

Originally Posted by BMR_LVR

Congrats. I was under the impression that a bad CPS basically caused the car to just not run at all. I learn something new everyday. Thanks for sharing the solution.

Steve

BTW, would you be kind enough to check the resistance on the failed CPS? I would be curious to know what the reading was. If it is in the normal range (540 ohms +/- 10%), then that makes the resistance check rather unreliable for establising the health of the CPS.

Just for the fun of it I tried firing up without CPS connected. Ran fine.

The resistance is 728 ohms. Not that my measuring device is the most accurate in the world, but it draws a picture, that the resistance is too high.

Umm ...... the car cannot run if the CPS (crankshaft position sensor) is not connected ... unless I am just totally off my rocker

Not sure what you disconnected, but I would track it down to figure it out.

Gald you got it running though.

Steve

Edit: Are you referring to the camshaft position sensor? The car will crank and idle fine if it is disconnected, but it doesn't do well going down the road from what I understand.

cpk, ckp= crank position sensor, cmp/cmps=camshaft in tech acronym jargon.

i get confuseded sometimes myself, so i look for the 'm' or 'k'. cam will be designated by the 'm', the crank by the 'k'.

and no, the car will not start without the crank signal. it will run poorly, though, if one if out of spec.

the cam position sensor is just for a synch signal to identify the #1 cylinder.

thanks for the update on this though. it'll help wihen others may be searching for answers to similar issues.



df

Originally Posted by BMR_LVR

Edit: Are you referring to the camshaft position sensor? The car will crank and idle fine if it is disconnected, but it doesn't do well going down the road from what I understand.

Hah, yea, i was referring to the camshaft position sensor. My bad. Dunno if it shows from my profile, but english isn't exactly my native...

The car ran smooth without the cam sensor, no hickups or the like. It's fascinating how the M50 can run without most of the sensors, they're all there for fine tuning Congratulationswelldone BMW

Gotcha. Glad you were able to figure it out and get it running. I agree that it's odd that you can have a bad sensor (camshaft position sensor) and the car runs poorly, but you can disconnect that very same sensor, and the car runs fine. I gues the quesiton is, how would it have run on the road without the sensor connected. I wouldn't try it though.

Anyway, glad you got it fixed and thanks for sharing the cause.

Steve

P.S.: What is the resistance on the new camshaft position sensor? Maybe that can give us all a baseline to work off of since Bentley left it out.

Originally Posted by BMR_LVR

Gotcha. Glad you were able to figure it out and get it running. I agree that it's odd that you can have a bad sensor (camshaft position sensor) and the car runs poorly, but you can disconnect that very same sensor, and the car runs fine. I gues the quesiton is, how would it have run on the road without the sensor connected. I wouldn't try it though.

Anyway, glad you got it fixed and thanks for sharing the cause.

Steve

P.S.: What is the resistance on the new camshaft position sensor? Maybe that can give us all a baseline to work off of since Bentley left it out.

The new position sensor measures 1244 ohm. My local parts shop states that the value should be 1400 +/- 10%. A bit out of range, but works just perfectly.

Crankshaft sensors on the other hand should measure 550 ohm +/- 10%.

^ sorry, i only speak cheese danish...


df

Originally Posted by drivinfaster

^ sorry, i only speak cheese danish...


df

Problem solved



Figured you'd see the "Modstand [ohm] 1400" Modstand = resistance.