help re rough idle...

[pong]

this is what my mechanic told me after a
couple of days searching for air intake leaks
which he could not find...

this two parts could be the culprit...

12621747281 engine coolant temp sensor
13621709966 temperature sensor...

was wondering... how can these two sensors...
which are related to coolant temp... make a
car idle rough... and at high rpms...

need quick help coz if i dont get this car to run well
im freaking gonna sell it soon... im close to the end
of the line...

thanks!

[Bin_jammin]

it's because the ecu is seeing a temp reading that is different from reality. I've seen temp sensors that read at -30F when they fail, so the ecu dumps tons of fuel into the engine to warm it up.

[pong]

is there a way to test these temp sensors?

[Bin_jammin]

is there a way to test these temp sensors?

Sure, you can boil 'em. You know water boils at 212, so stick it in a pot of boiling water, stick a thermometer in there so you have a reference, and put a meter on it to read resistance. I don't know exactly what the resistance readings are, but I imaging the bentley bible will have the exact procedure. Google around a bit, it's a pretty simple test.

[pong]

bentley says that the brown plug is the one that sends to the temp gauge on d dash... (170-3)

the dash temp seems to be working since once in a while... it goes a bit past d midpoint or acts normally as i heat up d engine...

d other plug... d blue one... i couldnt find info on it...
where could i find info on that in bentley?

bentley mentioned jumping the wires to simulate high temp...
(for d brown)

can i do d same for d blue?

[gale]

The blue one is the one that sends the temp signal to the DME, that's the one you want. Should measure about 270 to 400 ohms when at operating temperature. If you jumper it (short) it will make the DME run too lean and will stall at idle. You could stick the leads of a 270 - 400 ohm resistor into the connector socket, 1/4 or 1/2 Watt would be sufficient.

Bentley's has a segment for testing it. I measured mine a few years ago and noted resistance vs. temp:

http://www.bimmer.info/forum/attachment.php?attachmentid=5074&stc=1&d=1189359517

Also check the gap for the reference sensor/pulse sensor at the front of the timing cover at the harmonic balancer's toothed wheel. Should be about 1 mm +/- 10%. Sometimes the bracket will get loose and the gap can change. Have you tired a dose of injector cleaner (Techron concentrate, etc.) and a hard run on the highway to blow the cobwebs out of it? Carbon deposits on the tips of the injectors will cause idle problems. M20's are notorious for building carbon deposits on the back side of the intake valves which will screw with the idle. Again, a treatment such as Seafoam or BG44 & a hard run on the highway will help.

[pong]

was wondering... is that the same as d one for the m20?

[gale]

was wondering... is that the same as d one for the m20?
Yes. All the blue DME temp sensors are the same for the m10, m20, m30, m50, and numerous other M engines and was used in the e28, e30, e23, e24, e32, & e34 & perhaps others. As long as it has the same connector end fitting, it will swap from one to another. It's a thermistor, which characteristically measures around 2k ohms ambient, 200-400 ohms at typical engine operating temps.