TPS

[dsulu]

Hi Folks, it is been a while since I posted last time.

I have a 98 2.5 litre, 5-speed with 128K on the clock. For last 6 mo. or so, I started experiencing engine rough idle, stalling problems with no CEL. ( I know, it doesn't mean there is no code, thinking about buying durametric soon ~$280)

I took out the throttle body and Idle control valve and clean them. I also cleaned the MAF. The problem still persists.

I read several posts on the forum that point to bad tps. I have the following several questions.

1. Does a bad TPS trigger CEL always?

2. Is there a way to test TPS, voltage, resistance, etc?

As always, any help is greatly appreciated.

[wvicary]

Why are you thinking TPS? They are very reliable. You really need to check for fault codes and vacuum leaks.

[dsulu]

I will defintely visually check areas for possible vacuum leaks again, although I double checked everything when I put the throttle body back in after cleaning the tb and idle valve.

The reason why I thought the TPS might be the culprit is because of the symptons of the problem. on ocassions, below 1000rpm the rough idling, and then it stalls. ( regardless of temperature/ first few minutes of driving or after an hr of driving ) Also around 1500~2000 rpm, it feels lack of power.

Without code reader, I guess I am just trying to troubleshoot based on some common symptons.

I will try to get hold of one this weekend. In the mean time, any suggestion is appreciated.

[dsulu]

So there is a little update; called around local part stores to see if any of them would loan an OBDII reader or allow me to just use it while I am here. It seems that all of those auto part stores stopped loaning out OBDII code scanner. ( auto zone, o'reilly's etc )

So, I am back to just troubleshoot based on numerous threads from the forum.

The symptoms seem to be aligned with bad crankcase position sensor, and/or throttlebody position sensor. ( can't find any visible vacuum leak )

I found what Loren posted a while to troubleshoot the CPS

"

1. Remove connector. Connect ohmmeter to CPS connector, pins 1 and 2. Display at 20 °C: 0.8 - 1.0 kohms.If this is not the reading then replace the CPS.2. Connect an ohmmeter to CPS connector, pins 1 and 3. Display: infinite ohms.If this is not the reading then replace the CPS."

Is there a similar to troubleshoot the throttle body position sensor as well?

Any thoughts?

[Loren]

Throttle Position Sensor Trobleshooting

Check voltage supply to TP sensor.

1. Connect special tool 9616.2. Connect voltmeter to pin 53 (positive) and pin 34 (negative).Switch on the ignition. Display: approx. 4.5 - 5 volts

Check TP sensor.

1. Connect special tool 9616 to wiring harness (DME control module connector).2. Connect ohmmeter to pin 44 and pin 53. Display: approx. 2.0 - 3.0 k ohmsFully depress accelerator pedal. Display: approx. 0.7- 1.4 k ohms

If there is no display, check the throttle position sensor directly.

Check wiring from TP sensor to DME control module for continuity or short circuit to B+ or ground.

Note: The wires to the TP sensor are routed via connector X 59/2.

1. Separate disconnection point to TP sensor.2. Connect special tool 9616 to wiring harness (DME control module connector).3. Connect ohmmeter to disconnection point, pin 1, and special tool 9616, pin 34. Display: 0 - 5 ohms4. Connect ohmmeter to disconnection point, pin 2, and special tool 9616, pin 53. Display: 0 - 5 ohms5. Connect ohmmeter to disconnection point, pin 3, and special tool 9616, pin 44. Display: 0 - 5 ohms6. Connect ohmmeter to disconnection point, pin 2, and ground. Display: infinite ohms7. Connect ohmmeter to disconnection point, pin 3, and ground. Display: infinite ohms8. Connect voltmeter to disconnection point, pin 2, and ground. Display: 0 V9. Connect voltmeter to disconnection point, pin 3, and ground. Display: 0 V

If battery voltage is indicated for points 8 and 9, check wiring harness for chafing and pinching damage.

[dsulu]

Being busy for a few days, just got back.

Loren, thank you very much for the info. I don't know if the instruction provided is within my capability, I will try to find out what special tool is.

Once again, thank you for the quick reply.

[JFP in PA]

The tool (special tool 9616) is a Porsche "Pin out" or "DME break out" box for testing circuits. Porsche's Black Forrest version is about $2K (if you can find one), OTC makes something similar, but equally rare, called the OTC 3226:

This allows you to plug into the DME's wiring harness and test individual circuits electrical properties to make sure they are functional. All in, sells for about $1k.

[dsulu]

Thank you for the quick reply.

It looks like this "special tool" is out of my reach. Awesome info and picture.

I will just get the TPS out of the throttle body and clean it, if I could and use ohmmeter to test CPS this weekend.

Hopefully this will eliminate no starting, stalling and lack of power between 1500 and 2000 rpm problems.