Alright I'm new here so please point me in a direction if this subject matter is posted here somewhere.  I threw a TPS (along with a knock sensor and VSS) code in my 91 legacy I read in the chiltons that when testing the sensor that I should get a resitance of 12 kilo ohms throttle closed and 5 with the throttle fully open.  That being said I tested the one on my car along with about six others at the local junkyard (hair brain idea) and each sensor tested with a different ohm reading but I got the same resistance wether the was trottle open or closed, even the new one I just purchased.... WTF!  Did I miss something here?  Thanks in advance.

I think you are measuring across the wrong pins.  This should be a 4-pin TPS.  Let's ignore the idle switch for now.

 

The  variable resistor portion of the TPS works like this.   One "end" of the resistive element goes to the power supply.  The other "end" goes to ground. The "wiper" is a moving contact which slides across the reisistive element. You want to measure from the wiper to one of the end pins.  If you measure from end pin to end pin, the reistance will be constant regardless of the position of the throttle.

You really want to look for "dead" spots (i.e. the resistance should slowly and progressively change as you slowly open the thottle.) If it's jerky or the readings are erattic, bad TPS.

 

Good luck,

 

Nathan

I see, so maybe try testing pins 2 and 4 instead of terminals 2 and 3 like the Chilton says? That is where I get the constant resistance. Since you mentioned idle switch is it possible for a tps code to show because of a faulty idle switch?

As a side note I'm not the greatest electrical guy.

 

I just swap the throttle body - it's easy and simple.

 

I can have that done while I'm still trying to figure out what setting to use on the multimeter.

 

So you may want to think of this as an option.

I already got the new tps, just trying to understand a poorly written repair manual. I just checked the existing tps off pins 2 and 4 and got a decrease in resistance as I opened the throttle, the results were out of spec ( hence the new tps).

 

Davebugs maybe yinz should try the multimeter next time, just set the meter to just above the amount of resistance you expect to read n'at. i.e. tps should read between 10 and 12 kilo ohms throttle closed so set the meter to 20 kilo ohms and there yinz go. Just don't try to figure out what pins to measure off of from a Chilton manual.

I already got the new tps, just trying to understand a poorly written repair manual. I just checked the existing tps off pins 2 and 4 and got a decrease in resistance as I opened the throttle, the results were out of spec ( hence the new tps).

 

Davebugs maybe yinz should try the multimeter next time, just set the meter to just above the amount of resistance you expect to read n'at. i.e. tps should read between 10 and 12 kilo ohms throttle closed so set the meter to 20 kilo ohms and there yinz go. Just don't try to figure out what pins to measure off of from a Chilton manual.

I've come to realize that I can use a Mutlimeter for 2 things.  To set it on 20 volts to check batteries, and a setting I have marked to check resistance on my glow plugs on my VW's.  All the other settings mean nothing to me. Or more accurately picking another setting and trying to use it just leads to frustration.

 

Wiring and headliners are 2 things I learned years ago that I do not enjoy...  Infact I just picked up my 90 S10 with 37k from getting a new headliner and carpet this week.

 

I would like to learn to rebuild starters and alternators some time, and that's as electrical as I'd like ot get.  But I always have throttle bodies around so I just swap those out.  And it's easy for those of us who are challanged by the multi-meter.

jabbermen - if you plan on keeping your car a while, I would highly recommend tracking down a factory service manual for it - at the very least the "engine" section/book. Much better information than any Chiltons or Haynes manual will ever give, including step by step trouble shooting for each sensor with the correct values for each, how to test, and where/what terminals to test.

 

I have 3 of the 6 books for my 1990 model - engine section, for everything engine related, including CEL codes; body section for anything "body" related (windows, wipers, interior, etc); and electrical for the wiring schematics and even more electrical trouble shooting info - for things like cruise control, heater controls, etc - invaluable resources!

the 90 model had extra wireing conector for tps / tcu by the battery a clear 3 prong plug have seen them get coroded there and cause grief the sensers are perty reliabble have never changed one or seen a problem with tps

For the four pin TPS, checking pins 2 and 3 are definitely wrong assuming the diagram in Haynes is correct.

 

Pin 4 is the wiper. You could measure between 4 and 3  OR 4 and 2. The resistance readings will move in opposite directions. (i.e. one pair of pins will read max resistance with the throttle closed and min resistance with the throttle open.) The other pair will read min resistance with the throttle closed and max resistance with the throttle open. You're really looking for a smooth, consistent change in resistance as the throttle is opened rather than a specific number.

 

The idle switch is between pins 1 and 2. It should have continuity (zero ohms or close to it) with the throttle closed and should be open (no continuity) when the throttle is open. To adjust it, you're supposed to put a .028 feeler gauge between the throttle stop screw and the throttle stopper. The idle switch should still be closed. With a .035 feeler gauge, it should be open. 

 

Nathann