What does it control? Where does it go and why will my car only run well when I tie the switch back in the idle position? Late 89 xjs

 

I did some wiring diagram research....

The idle switch is inline on the wiring to the "Strategy Selection Link". A bit of explanation...

The Strategy Selection Link is essentially a loop circuit with a removable connector. When the connector/plug/link/whatever is *removed*, the loop becomes an open circuit and the timing is retararded to allow use of lower octane fuel.

Since the idle switch is inline on one of the wires of the SSL, opening the switch gives the same result as unplugging the connector....the loop goes "open circuit" and the timing is retarded. Closing the switch completes the circuit, obviously.

I *think* the switch is supposed to be open at idle and closed just off-idle. I can't be sure....

I know the switch is supposed to be adjusted to actuate *just* on the edge, so to speak, of open and closed throttle. I'm not sure if the switch is normally closed and actuating it opens the circuit, or if it is normally open and actuating it closes the circuit.

I'll try to find out more or hopefully someone else will chime in with more info.

But....the switch DOES change the ignition timing.

Cheers
DD

 

Thanks doug. It almost seems as though my switch is working in reverse of what it should . What you wrote makes sense. I read about something at the ECM the can be switched to run lower octane fuel. I just wondered if this was switched improperlly at the ECM ? Thanks for your wisdom and efforts

 

Is that the micro switch on the the left side of the engine at the rear bell crank? If so, that switch is supposed to send a signal to the ECU or EFI (not sure which one) that the engine is at idle. At idle the switch is closed. Apparently, this signal tells the the engine to ignore the MAP input signal to avoid "ping" . Got this information from a service manual for 1990 XJS with the Marelli Ignition. Also, your switch may be defective. Try isolating the switch and testing it with an ohm meter. You cam also manually join the two wires that were on the switch, and then retest your engine.