Engine Speed Sensor Question

[betsy325e]

Whazza, driving enthusiasts/gluttons for punishment?

Still trying to track down high idle. I noticed that the connector on my Engine Speed Sensor is absolutely destroyed. From what I understand it counts teeth on the flywheel by magical magnetic somethin' or other. I understand that that information is then sent to the ECU and the idle control module. Did the ohm test: 960 +/- whatever. Seemed fine.

My question is, what does this engine speed sensor actually do, and, when operating normally, what is it telling my ECU/ICM to do?

Thanks.

J

[jlevie]

The reference to an ICM makes me think that this is a E car. In which case both the transmission mounted speed and timing reference sensors are probably overdue for replacement. There is a front mounted speed sensor, but it is only fordiagnostic purposes.

The purpose of those sensors it to tell the DME/ICU what the engine speed and timing are in order to control spark & fuel. In most cases a high idle will be due to intake leaks or a bad ICM. Have a smoke test run.

[betsy325e]

Jlevie,

1987 325e.
I asked because I remember reading something somewhere about the speed sensor failing causing the car to go into some sort of "limp" mode. This morning I had my #3 and #4 fuel injectors miswired. Rectified the situation and still ran exactly the same. Made me wonder if the car is in that "limp mode." I don't even know if such a thing exists. Just spit balling (getting desperate as you can see from this thread):

http://www.r3vlimited.com/board/showthread.php?p=4450478#post4450478

Have you ever heard of such a limp mode setting being caused by a failing speed sensor?

Thanks,

J.

[TobyB]

The e senses engine position/speed from 2 sensors in the bellhousing, reading off
cuts in the flywheel.

the sensor in front is just for diagnostics, and isn't used by the ECU on the eta...

t