1998 Chrysler T&C Throttle Position Sensor Readings

[loots42]

I have a 98 T&C 3.8.

When I'm driving down the road, the rpms seems to slightly increase for a second or 2, and then go down. I put my brothers scan tool on it, and the throttle position sensor reading is 12.5 without pressing the gas pedal at all. It read 72.5 with the pedal mashed to the floor. This seems odd. Shouldn't it be 0 and 100 respectively?

Is my TPS at cause for the increase in rpms?

[RIP]

12.5 and 72.5 - What's the unit of measurement? The only way I know of to test a TPS is to connect a multimeter and read the voltage output. Should read .4 to 1.2 vdc with the throttle closed, 3 to 4.5 vdc wide open. The PCM supplies the 5 volt reference voltage. If your measurements are voltages then they are invalid. Use a multimeter and backprobe the TPS connector to measure the voltage.

What you're seeing is called a surge. Is this surge cyclic or random? What happens when the cruise control is on? One common cause for a surge is a vacuum leak.

[loots42]

The measurement is percentage. I hooked the same scan tool to my GMC Jimmy, and it ranges from 0 to 100. So it seems likely to be the TPS?

Do I have to take the upper air plenum off to change the TPS?

Thanks.

[RIP]

Not sure this is a valid correlation, but if 0 vdc = 0% and 5 vdc = 100% then the acceptable voltage ranges I gave you would indicate that no, it "shouldn't be 0 and 100%". If you accept that, then the 12.5% and the 72.5% reading you got looks within the range. After the math 12.5% = .625 vdc and 72.5% = 3.625 vdc. Both voltage readings would be within the acceptable limits. All that said, another thing to watch for is spikes or drop outs as you move the sensor.

The TPS is on the aft upper side of the throttle body. Shouldn't have to remove anything but maybe the intake duct at the throttle body. May be easier if you remove the throttle body itself.