TPS at Idle

[akorna]

Been troubleshooting an intermittant miss at idle - '99 Cherokee 4.0 Auto 4X4. My OBD II scanner shows that the TPS is sending a signal of 15% throttle opening at idle (even though I'm not pressing on the throttle). Signal voltage form the TPS with the ignition off is 0.78 votls (within the 0.26-0.95 volt range. Shouldn't the TPS show 0% throttle if you're not pressing in the throttle?

Anybody else show more than 0% at idle?

Thanks!

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[y2kxj]

All I can see in the Haynes manual is a check using a high- impedance digital volt meter. Connect the positive probe to the center terminal and the negative probe to the ground terminal(black wire). (Note: This is done by back probing the electrical connector(don't unplug the connetor from the TPS). With the ignition on, slowly move the throttle lever until it is wide open and observe the reading on the meter. With the throttle fully closed it should read greater than 200 millivolts. With the throttle fully open, is should be a little less than 4.8 volts. If the voltage readings are incorrect, replace the TPS. It doesn't make any reference to what it should be at idle.

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[XJNick]

Originally Posted by akorna

Signal voltage form the TPS with the ignition off is 0.78 votls (within the 0.26-0.95 volt range.

This doesn't make sense -- there should be no power present at the TPS if the ignition switch is OFF.

The correct working range of the sensor is 0.8 - 4.8 volts.
This means with the throttle CLOSED you should read 0.8 volts.
This means with the throttle WIDE OPEN you should read ~4.8 volts.

You need to adjust the resistance of the sensor at closed throttle so it outputs as close to 0.8 volts as possible. This is done by loosing the bolts and pivoting the sensor until the voltage is correct. ALWAYS do this adjustment with the engine OFF, but the ignition switch in RUN.

-Nick

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[akorna]

Guys - Thanks for the reply. I typed faster than I was thinking. The voltage tests were done with the ignition on. ALLDATA for 99 Cherokee says range with throttle closed should be 0.26-0.95v. That compares with the "greater than 200 mv and 0.8v specs you passed on. My TPS meets the spec requirements - just puzzled why the scanner shows the throttle is 15% open. My other OBD II vehicles show 0%. Something is off.

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[XJNick]

Originally Posted by akorna

ALLDATA for 99 Cherokee

Ahh... I missed that it's a '99 Cherokee. That'd be why yours has a different range -- it's OBD-II

-Nick