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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.

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

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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.

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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?

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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.

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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.

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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:

Picture+0041187479716.jpg

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.

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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.

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