1991 Subaru

[Tech]

1991 Subaru Loyal
Fuel Injection
4 cylinder
Automatic

Need some thoughts on what would cause this car to stall out when trying to pull out, it act's like it want take off then take's off... and while in motion driving it.. as long as you keep the gas pedel down and going ok your fine... can feel a slight hesitation, but if you let off the gas and very give it gas while driving it... it continues acting up .. acting as if it want go then all of a sudden takes off... keeps doing that over and over if you do not give it alot of gas?

any advice would sure be appreicated...

[DanD]

I’m not too familiar with Subaru so I’m not sure what to say other then check the TPS (throttle position sensor) it, like its name tells the computer throttle position as well as the rate of change in throttle position. If it’s not sending this signal; the computer will not know to enrich the fuel mixture to allow smooth acceleration.
Most TPS are a three wire sensor one being reference voltage sent by the computer, sensor ground and signal return.
Reference voltage is usually 5 volts; signal return varies from about .5 (1/2) volt closed throttle to around 4.5 volts wide open throttle. This variable voltage should change smoothly and evenly as the throttle position is changed.
You can test this with a voltmeter connected to the return circuit by back probing the TPS connector and to a known good ground. Turn the ignition on and move the throttle through its range while you watch the meter. If the voltage doesn’t change or does not scale up evenly as you move the throttle the sensor has gone bad.
As for which wire is what I don’t know but you won’t hurt anything by back probing all three until you find the return.
I’ve found that a safety pin works well as a back probe, it can easily be slid up the back of the connector beside the wire until it touches the metal terminals inside the connector with out do any damage to anything.
No doubt there are a lot of other things that can cause this problem but at least you can rule out the TPS by testing it.
Dan.