Behavior of throttle switch / check procedure ‘89 m20

[r-mm]

I checked and adjusted the ‘off’ function of my throttle switch per bentley. Works exactly as described. Then I went to check the full throttle function. Bentley says open the throttle slowly. When i do that everything checks out - continuity towards the end of the throttle’s travel. However when i took my motor out the stomp test wasnt working. I simulated a stomp by opening the throttle quickly by hand and got uneven results. The ohms dropped but not always enough to trigger the continuity tone.

Has anyone encountered this?

[earthwormjim]

Is your throttle cable adjusted properly? Perhaps the cable is too tight and doesn't let the throttle close completely?

Did you clean the throttle too? Carbon build up can cause it to stick a little. Might help to lubricate the spring and mechanism a little too.

Also clean the engine harness side of the TPS connector. Since oil readily flows into the TPS, it's possible it also got onto the connector contacts and is messing with resistance readings by the ECU.

You might also want to adjust the switch such that you give it a little margin for detecting when you are off the throttle. It's not likely you will actually use 5% throttle, so why not adjust the position such that say 5% or under clicks over to the closed resistance value? The switch needs to account for the throttle position when cold and hot, so there is some variation there.

[r-mm]

Behavior of throttle switch / check procedure ‘89 m20

I am bench checking the switch per the photo so none of the other elements are a variable here. Just the switch and throttle which is nice and clean, lubed.

Bentley calls for the switch to be adjusted so that there is continuity when the throttle lever is .2 to .6 mm from it stop. I adjusted it that way.

[r-mm]

To be clear the throttle closed switch works perfectly. Its the WOT part of the switch that seems ‘speed dependent’ ie it doesn’t give rock solid performance if i snap it open but does if i ease it open.

[earthwormjim]

Oh, I thought you said you were doing stomp testing after bench testing the throttle.

Maybe your throttle stop screw is set to leave the throttle too far open? If the throttle is too far open, then the available range of travel is limited, which might cause problems with the position switch detecting WOT.

To adjust the screw, loosen it so that it is flush with the arm it mounts into. Then tighten it 1/4 turn. I suggest marking the current position of your screw, so you can restore it to where it was before you started messing with it, just in case adjusting makes no difference.

[ForcedFirebird]

Oh, I thought you said you were doing stomp testing after bench testing the throttle.

Maybe your throttle stop screw is set to leave the throttle too far open? If the throttle is too far open, then the available range of travel is limited, which might cause problems with the position switch detecting WOT.

To adjust the screw, loosen it so that it is flush with the arm it mounts into. Then tighten it 1/4 turn. I suggest marking the current position of your screw, so you can restore it to where it was before you started messing with it, just in case adjusting makes no difference.

This. If the stop screw has been messed with by a previous owner to keep it slightly more open than stock, the WOT switch may never be initiated once the TPS is adjusted. We had this recently at the shop. That screw is only to keep the throttle plate from getting stuck when slammed shut, should never be adjusted to raise idle.


I would suggest setting the stop screw first, then moving on to adjusting the TPS switch.