TPS Testing

[Garsdad]

I have read the post on testing the TPS and have a couple of questions.

First, on my 91, the top wire is a constant 5 volts, the middle is the ground (black, and confirmed ground by a continuity test to the ground on the battery) and the bottom reads nothing, or 12 volts, depending on throttle position. This is different than most of the things I have read, where the top wire was listed as the ground.

There is no varible voltage reading with movement- it is all or nothing. Top wire goes from 5 to zero as you approach WOT- as expected. The bottom wire goes from zero to 11.67 with a couple of degrees of movement off idle, then stays there for the rest of the range of motion. Nothing variable.

When I checked for resistance, it was all or nothing again. I went from zero resistance to no current flow within a couple of degrees motion off idle, and nothing in between.

I'm guessing that this, combined with the inability to idle without a significant amount of throttle added, means that after 21 years and 152000 miles my TPS has sensed its last throttle position.

Am I missing anything here?

[scitzz]

Detach the connector from the throttle position sensor.
Connect an ohmmeter between terminals IDL and E.
Insert a 0.004 in. (0.1mm) feeler gauge between the throttle stop screw and stop lever.
Verify there is continuity between terminals IDL and E.
Then replace the feeler gauge with a 0.02 in. (1.0mm) feeler gauge, verify there is no continuity between terminals IDL and E .
Then open the throttle wide and verify there is no continuity again between terminals IDL and E.
Next, connect the ohmmeter between terminals POW and E.
Insert a 0.004 in. (0.1mm) feeler gauge between the throttle stop screw and stop lever.
Verify there is no continuity between terminals POW and E.
Then replace the feeler gauge with 0.02 in. (1.0mm), verify there is no continuity between terminals POW andE.
Then open the throttle wide and verify there is continuity between terminals POW and E.
If not as specified, adjust or replace the throttle sensor.

The tabs, top to bottom, are

POW
E
IDL

[georgeb]

Sounds like the idle portion only detects idle...on or off. Your's might be okay.

[scitzz]

You can adjust the idle screw, and see if that helps. Also, be sure the IAC is plugged in. My TPS is original, after 750K, and 19+years....As htchbck told me, they are very simple devices, really. Not much to go wrong with them.

[Garsdad]

So it only tells the ECU "It's at idle, It's at WOT, or It's somewhere in between" ? The only other vehicle I have ever had to mess with the TPS on was my Moto Guzzi, and the signal varried across the whole range of motion so the ECU would know exactly how far open the throttle was.

This one is simply two switches to show three phases of operation (Idle, WOT, and not idle or WOT)?

[georgeb]

Sounds like it has two circuits. One for idle on or off, and another variable one for throttle position.

[htchbck]

At idle there should be continuity between middle and the idle pin. At WOT there should be continuity between the middle and WOT. Anything in between there should be no continuity.

[Garsdad]

Update, new question:

I tested the TPS, and it passed all of the continuity test. Borrowed a Haynes manual from the library, and they detailed a voltage test. It failed that test miserably, so I bought a new TPS. Before installing it, I plugged it in to my car's harness and got exactly the same results. I returned it; thankfully Autozone doesn't have an "electrical parts can't be returned" policy. I checked a few dozen little things, like vacuum leaks, etc. Put the jumper wire in and got two codes- the intake air sensor and the airflow sensor. The way the manual says to test it is to back-probe the harness with the engine running... it won't run, so this is not an option (OK, it runs, but only if I keep the throttle open).

Is there a way to test this component statically? Would unplugging the unit, turning the key to "on" and testing for reference voltage cause it to throw the code? How do you clear the code when using a jumper wire to obtain it?

The problem is it is running so rich it drowns the motor at idle. The stink from raw fuel in the exhaust is a good giveaway, along with the burning smell from the cat when I got home from work the last time I drove it.

Lots of questions, but I need to be able to get to work in the morning and this is the only car I have.

[georgeb]

Check the VAF connection or get a good used VAF.

[jimdigs]

Detach the connector from the throttle position sensor.
Connect an ohmmeter between terminals IDL and E.
Insert a 0.004 in. (0.1mm) feeler gauge between the throttle stop screw and stop lever.
Verify there is continuity between terminals IDL and E.
Then replace the feeler gauge with a 0.02 in. (1.0mm) feeler gauge, verify there is no continuity between terminals IDL and E .
Then open the throttle wide and verify there is no continuity again between terminals IDL and E.
Next, connect the ohmmeter between terminals POW and E.
Insert a 0.004 in. (0.1mm) feeler gauge between the throttle stop screw and stop lever.
Verify there is no continuity between terminals POW and E.
Then replace the feeler gauge with 0.02 in. (1.0mm), verify there is no continuity between terminals POW andE.
Then open the throttle wide and verify there is continuity between terminals POW and E.
If not as specified, adjust or replace the throttle sensor.

The tabs, top to bottom, are

POW
E
IDL

The manual states to use a .5mm (0.020) then check to make sure there is continuity not a (0.004) like you state in your reply plus your other numbers are off from the manual as well. Just wanting to know if I'm missing something here as I want to check my tps. thanks, Jim