Throttle position sensor

[mmcgehee9989]

I'm a new member and I just sold my 85 Z-28 and purchased a 93 Trans Am with the LT-1, bone stock with 100,000 miles. After driving it for a while I notice the engine sometimes hesitates when I give it gas either from standstill or on when I'm already underway. I've asked around and was told that the TPS sensor might be fouled up. Does anyone know how to diagnos it without taking it to the dealer or a mechanic shop.

[N20LT4Bird]

A scanner is nice for looking at TPS activity, but if you dont have access to one, you can probe it with an ohm meter and look for a "dead spot". The TPS is not much more than a potentiometer or a variable resistor. As throttle angle changes, resistance changes. Probe the sensor with an Ohm meter while twisting the throttle. Look at the sweep and make sure the resistance varies equally with throttle movement. If there is a "sticky spot" (where resistance doesnt change), there is your hesitation. A hesitation can be caused by variety of other things as well.

[Injuneer]

With key in the "on" position, measure the voltage across the dark blue (pin "C") and black ("B") wires. At closed throttle, it should read between 0.20 - 0.90V. It doesn't have to be a specific value, because the ECM measures the closed throttle voltage, baselines that as 0% throttle position, then prorates up from there.

After you measure closed throttle volts, move the blades to wide open, and measure the volts again... should be approx 4.0V above the closed throttle voltage.... e.g. if closed was 0.60V, WOT shoul be around 4.5 - 4.6V.

Then watch the voltage as you slowly rotate the blades from closed to open. Voltage should increase smoothly, with no spikes.

Some people seem to feel that even though the TPS sensor on the LT1 is not adjustable, they get best performance with a closed throttle value of 0.50 - 0.67V. If you want to adjust it, you need to slot the screw holes in the TPS so it can be rotated to adjust the volts.

[mmcgehee9989]

To N20LT4Bird

You said a hesitation can be caused by a variety of things. Like what?

[N20LT4Bird]

If you have an SES light on, start there and get it scanned. You could also have fuel delivery issue (clogged fuel filter, dirty injectors), clogged air filter, vacuum leak(s), or possibly an ignition sys. issue; all of which may not trip an SES light. Without actually driving it and looking at it, its very hard to say. It could be a troubled TPS or something else like I just mentioned (and I am sure we could add to my list). A scanner is a most helpful tool in these instances allowing you to look at things like your O2's (to see what your fuel delivery is like) timing advance, IAC counts, TPS voltage etc....

Let me know how the TPS turns out. You can check actual voltage to the TPS like Injuneer has said or check resistance through the sensor. Your essentially doing the same thing. Injuneer has provided some exact voltages to look for which will help you to determine whether or not the sensor is "set" right at closed throttle. This is very important, but in my experience a TPS that couses a stumble or hesitation will have a "dead" spot. Check for it. Get back and post yor results.

[mmcgehee9989]

Appriciate it. I'll let yall know.