[mdss]

Hi guys would any of you know what voltage the throttle position switch should show at closed throttle. Mine is showing 0.7 volts which i thought was a little high and having done a vacuum test as flash suggested which showed no leaks re:my cold start rough idle i suddenly thought i wonder if the switch is advanced a little.



Most cars are usually aroun 0.2-0.3volts at closed throttle



Once again thanks in advance for any help.

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[Cloud9...68]

You're in luck - I just happen to have tested my <acronym title='throttle position sensor'>TPS</acronym> several years ago as part of the troubleshooting of a hesitation problem I was having, and I got this test procedure from somebody off the old .net:





The 968, like most all cars uses a true throttle position sensor. A variable resistor that can read out to the ECU the exact position the throttle is in. There are 2 ways to test it. Connected, and disconnected.

First the connected way: turn the ignition on, but don't start the car. you'll have to have some type of voltmeter probes that can make connections without unplugging the connector. Usually you pull the boot off the back of the connector, and push the probes in there. If i'm reading the wiring diagram correctly, you should find 5V on pin 2 (the blue/green wire) pin 1 should be ground (the yellow/brown wire) and pin3 is the output (the white/green wire). To test, you should hook the voltmeter between pin 1 and 3. as you slowly open the throttle, the voltage should go from about 0.4V to 5V with no abrupt jumps, either up or down. Abrupt jumps are a sure sign of a bad <acronym title='throttle position sensor'>TPS</acronym>. An old, analog voltmeter is MUCH, MUCH better at seeing intermittent jumps than a digital one, but who the heck has one of those.

To test the disconnected way: uplung the <acronym title='throttle position sensor'>TPS</acronym>, and hook a ohmmeter between pins 1 and 3. slowly move the throttle open and you should see a smoothly changing resistance value. I don't know what the range should be, but again, smooth changes are the important point here.

The disconnected way should be a little easier, but the connected way is more accurate.



As you can see, the voltage in the "off" (closed throttle) position should be 0.4V, so it sounds like yours is a little high, as you suspected. Good luck.

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[flash]

aha! while i was looking at vacuum as the culprit, i also said to check the throttle body - the idea was that the air quantity was wrong - so, looks like i was on the right track

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[mdss]

Hi guys quick update:

Adjusted the voltage and now its even worse i set it to 0.4 and now the car wants to nearly stall even once warm unlike before when it would only do it when it was first turned on in the morning.

I think now the only thing left is the idle speed control valve i know flash said its unlikely but nothing else left to check now.

Will report back tomorrow when it done.



Ah the joys of old porsche ownership..............!

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