BAD ECU ??- no change with mixture adjustment
 

Hello,
In an effort to find exactly why my car is running on only 4 cylinders, I may have found at least some proof my ECU is kaput. While the engine is idling, if I turn the mixture adjustment knob on the ECU, there is absolutely no change in engine perforemance. Shouldn't there be a big change when I turn the knob from one extreme to the other? Thanks. -Mike

Not if your throttle switch is open or open circuited.

So if I understand correctly, since at idle the throttle valve switch should be closed, it may be out of adjustment or the wires/connections or switch itself may be defective instead of the ECU? -Mike

Can't say what you got but I can say that if you disconnect the throttle switch the idle compensation adjustment you are turning won't work. Since it is only for idle mixture compensation when the idle switch is open the adjustment doesn't do anything.

This simple fact forms the basis for the method I have adjusted those D-Jet systems for near 30 years. The system base mixture is adjusted on the MAP sensor. To do this at idle I disconnect the idle switch which takes the comp circuit out of the picture and I can adjust what will be forming the mixture down the road. Set it to 1-2%CO and plug the idle comp back in and adjust to best idle. All after setting the timing to at least 5deg over factory spec.