I cleaned thoroughly the throttle body of my 1989 3.6. I removed the throttle position sensor (TPS) but I marked its position when I put it back. When I had installed everything back to the car and started the car the idle was around 1500 RPM. It was around 800 RPM before the throttle body removal and clean-up. I wonder what could be the reason for the high idle. I tried to lower the idle by adjusting the idle speed by following the instructions on the Ebook (below). I turned the idle speed air bypass screw on the iscv about two rounds to get low enough idle. When I hooked up the iscv connector the idle did not change. So, I thought the high idle problem was gone. It was not. When I turned off the car and started it again the idle was high again. In addition, I tried to adjust the TPS by turning it but its physical location in the throttle body seems not to matter. All the vacuum hoses are attached, and I can’t find any logical reason for the high idle. Are there any ideas what could be the problem?
10.6 - Adjusting Idle Speed
Set the throttle plate gap to .002(.05mm). This is the gap between the throttle plate and the wall. To do this right, you should remove the throttle body and clean it with some throttle body cleaner and then set the gap. The throttle body/ plate gets gummed up from the crankcase vent being before the throttle.
After setting the gap, reassemble the throttle body and all parts, clamps, wires, etc.
Warm up car,
ac off,
transmission in park,
turn key off,
Turn key on but don’t start car and wait 15 seconds then disconnect connector to iscv.
The iscv is just forward of the throttle body, close to the cruse control bellows.
turn key off,
hook up iscv connector,
turn key on but don’t start car…wait 15 seconds,
disconnect iscv connector, (your winding the iscv closed)
leaving the iscv connector disconnected, start the car.
turn the idle speed air bypass screw on the iscv using a 7\32 inch Allen wrench till the rpm is 550 to 600.
Hook up the iscv connector.
Robin, that sounds logical. However, I can’t see where the vacuum leak could be. I put everything back as they were. There are four vacuum / PVC hoses: two small vacuum hoses on the right side of the throttle body, one hose on the right side of the “EGR” (below), and one on the left side of the EGR.
Ok, Robin, so, I will spray the starter spray around the inlet manifold when the engine is running and probably I will then see if the RPM changes somehow and that may lead me to a possible leak.
I sprayed starter spray to the inlet manifold but I did not notice any difference in the RPM.
After that I removed the wire from the sensor in the elbow between the MAF and the throttle body. That did not make any difference. I also removed and cleaned the IVAC unit. I suspect that the TPS is faulty. I get intermittent “Check engine” warning on the dash. This is the first time I get this warning with this car.
The “check engine” light may help your troubleshooting.
Did you determine the code ? When the light comes on and it’s time to turn off the engine only turn the key off to the first position, do not turn it all the way off. Now press the VCM button and it will display the code. On your 89 model it will be a number 1-8.
Dennis, thanks for your tip. I have to check the code.
I plugged off the wire of the TPS and it did not have any effect on the RPM. So, I guess there is something wrong with the TPS. I checked that the wire that connects to the TPS plug has 5 volts. I have not checked the voltage on the TPS plug side.
Otto - you more than likely know this, but as I understand it, the TPS “sends” the resistance value of the wiper inside the TPS (which, if the TPS is set correctly, corresponds to the throttle butterfly opening) to the engine management computer. The signal increases or decreases the injector pulse length dependent on the position/signal.
If you disconnect the TPS and move the butterfly with the throttle cable, the computer won’t know and will continue to deliver fuel as if the throttle were closed and at idle. Air intake will be out of proportion though and a overly weak mixture will result, possibly throwing another code at the same time.
Dennis, I drove the car yesterday evening but I did not get the “Check engine” light. The car drives well, but the high idle (1500-1800 RPM) is annoying, of course.
Larry, I only disconnected the TPS to see if it has an effect on the RPM. But it did not. I did not pull the throttle cable nor drove the car.
I am now waiting information whether an independent Jaguar specialist has a TPS. It would be interesting to test the operation with another TPS.
Thanks for the good tip, Dennis!
I checked the voltages. The reference voltage was correct, 5 volts, but the signal voltage was only 0.04 volts and it did not change even if I rotated the potentiometer. The voltage should be approximately 0.5 volts. So, most likely the potentiometer is broken.
Robin, that is good for the new TPS type. I have the old type. I drilled three 2.5 mm holes to the cover of the TPS and sprayed carburetor cleaner into the TPS. That did not help. Probably I will open the TPS even if it can’t be done without damaging the cover.
This is the old type:
I put everything back as they were. There are four vacuum / PVC hoses: two small vacuum hoses on the right side of the throttle body, one hose on the right side of the “EGR” (below), and one on the left side of the EGR.
…