Help me diagnose this problem

[BlackE30]

So this has happened to me 2 times in the last week of driving my car. Sitting at a light my idle will just randomly jump like I revved up the car. It will jump up about 1,000 rpm. Today it did this but only once. Also when driving it will all of the sudden just start revving between 2500 and about 3000 jumping back and forth. It just did it to me on my way home, was going back and forth for about 45 seconds, just as I was going to pull in my court and check things out it went back to normal again.

Right before it happened I had just did a quick romp up to 60, slowed down to the 45 mph speedlimit and I could feel the car still wanting to accelerate. I pushed in the clutch and the revs started jumping between 2500-3000 or so. It makes driving a bit interesting.

Any ideas?

[BlackE30]

Anyone have any ideas?

[7pilot]

Perhaps you could check the resistance values at the ICV, and at the TPS.
Also check for an unmetered air leak, particularly anywhere on the intake tract on the engine side of the HFM. See if the engine rocking on acceleration/deceleration is opening/closing a slit that is driving the DME and ICV nuts.

m

[z31maniac]

ICV and vacuum leaks are where I'd start.

[jeff_b]

stomp test 1st. see if the car can tell you where to start. i suspect coolant temp sensor (to ECU) or ICV.

[BlackE30]

Interesting that you said the coolant temp sensor. I just replaced it last year and it threw that code when I did the stomp test yesterday.

[BlackE30]

Just want to double check- this is the right sensor for an obd1 swapped s52 correct -

http://bmaparts.com/ShopByVehicle.epc?q=&yearid=1995%40%401995&makeid=BMW%40%40BMW%40%40X&engineid=1013230%40%40M3++%2F+L6-2990cc+3.0L+GAS+FI++%28S50%29%40%40M3&keyword=sensor&subcatid=Water+Temperature+Sensor@@Water+Temperature+Sensor%2FFuel+Injection&mode=PA

[jeff_b]

link fail. brought me to the top of a menu tree to select parts for a 95 M3.

I'm not sure about the S52, but if you're running the typical M20 OBDI, there are two sensors; one for DME, one for gauge. They are independent of each other, and are a negative temperature coefficient type: engine temp up; sensor resistance down. I don't have the chart to correspond engine temp to sensor ohmic value. Seeing how the result is erratic engine running, if the sensor is fucked, I'd get the motor up to temp, and when it starts running like shit, pop the cap and read the resistance across the sensor. If you read varying or jumpy resistance, I'd guess it's fucked. It may not be the sole cause of your issue, but it's a start. Good luck!

[416stroker]

The coolant temp sensor fixed mine with the same symptoms. Fuck it you can get the fae one for $8 just change it.

[BlackE30]

The sensor that I linked to was for an obd1 s50. Assuming that's the one I use since my car is obd1 s52

[7pilot]

The sensor that I linked to was for an obd1 s50. Assuming that's the one I use since my car is obd1 s52

Since you have a young sensor, maybe a continuity check between the sensor plug terminals and the DME plug, for a broken wire.

problems is, your symptoms don't match the behaviour expected from a bad coolant temp sensor circuit.


m

[416stroker]

The sensor that I linked to was for an obd1 s50. Assuming that's the one I use since my car is obd1 s52

this is the oem P/N 13621709966

[416stroker]

Since you have a young sensor, maybe a continuity check between the sensor plug terminals and the DME plug, for a broken wire.

problems is, your symptoms don't match the behaviour expected from a bad coolant temp sensor circuit.


m

Its an electrical part age doesnt matter they just fail. Mine did and it was less than a year old.
And his syptoms are pretty close to what I had.

[BlackE30]

Here is the sensor I pulled out -

[sharky]

wrong sensor, you need a brown single pole E30 one and a blue one from a M/S 50