[John Wood]

The older electronic speed sensors on EEK cars were functionally the same... until they went to the Hall-Effect units in the early 90's (about 1992 to 1993). For the older units, you basically had a sealed unit with a micro switch that produced 8 pulses per revolution... i.e contact closures.

Depending on the car (you didn't give us the year), the computer used the speed sensor to determine when a moving car has come to a stop. The computer then adjusted the AIS motor to set the idle speed. A malfunctioning speed sensor could create a stall or stumble at that point, and usually a code 15 was stored.

The most common cause of the code 15 was a bad connection at the speed sensor plug. Later there were improved connectors to help improve that situation. Occasionally you could get an internal problem in a speed sensor and have a hard failure. Assuming you had an electronic speedometer, it would fail to register along with the odometer.

Some of the earlier speed sensors were a hybrid type that had the mechanical drive for the speedometer/odometer but also had the pulse contacts for the computer to use and for cruise control module.

Regarding the pinion gear, the different # of teeth on the different color gears was for speedometer/odometer calibration for different size tires or differential gear differeneces.

 

[torgtoe]

My car is a turbo z 86. Analog dash.

No code is seen.

when the problem was there- speedometer still worked-

i quess i may have a week wire, impossible to find.

But as you say, the AIS motor is involved in this, at it may be some dirt og damage in the ais-motor. Sometimes rpm rises for no reason.

 

[John Wood]

Do you know if the 86 turbo in your car uses a shutter type AIS? They can be more troublesome than the pintle type. The speedometer should be cable driven so it should always work irregardless of the pulse output condition from the speed sensor. I think in 87 they used the pulse output to drive the speedometer.

Check on minimopar.net. They may have a discussion of the shutter type idle control motor if that is applicable.

 

[Bob Lincoln]

The 86 would be the shutter type, and they are temperamental.

 

[torgtoe]

temperamental? :scared: