What could this problem with my car be?

Question

When I start my 1991 Pontiac Grand Prix SE and it's still in park, the engine starts racing like crazy. And I don't even have my foot on the gas when this is happening. Also noticeable when the engine is racing, is that the RPM gauge goes up high. I was told by a mechanic friend that it probably means I need a new throttle sensor. Is this accurate, and it not, what else could the problem be?

Answer 1

the problem with your car seems to be the idle speed control located on the throttle body also check for a massive air leak that can also rev-up your engine out of control

Answer 2

TPS Testing and Adjustment

The TPS is there to tell the ECU how hard you have your foot on the gas. It isn't there to adjust for the idle. It's a sensor. It does have some adjustment of it's own and we'll try to give our version of what our Factory Manual says (though we won't even come close to doing it justice):

Throttle Sensor & Soft/Hard Idle Switch

The Throttle Sensor responds to the accelerator pedal movement. This sensor is a kind of potentiometer which transforms the Throttle Valve position into output voltage, and emits the voltage signal to the ECU. In addition, the sensor detects the opening and closing speed of the Throttle Valve and feeds the voltage signal to the ECU.

Idle position of the Throttle Valve is determined by the ECU receiving the signal from the Throttle Sensor. This system is called "Soft Idle Switch" and controls engine operation such as fuel cut. On the other hand, "Hard Idle Switch", which is built into the Throttle Sensor unit on the A/T equipped models, is not used for engine control.

Trouble Diagnoses:
1. Disconnect Throttle Sensor harness connector.
2. Make sure that resistance between terminal #1 and #2 changes when opening the Throttle Valve manually.
Looking at the "pins" of the connector w/ the locking tab of the connector pointing up, terminals #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

The results of the test should be:

Accelerator Pedal Condition Resistance in k Ohms
Completely released Approx. 2
Partially released 2 -10
Completely depressed Approx. 10
If test shows "No Good", replace Throttle Sensor.

Adjustment:

If Throttle Sensor is replaced or removed, it is necessary to install in proper position, by following the procedures shown below:

1. Install Throttle Sensor body in the Throttle Chamber. Do not tighten bolts. Leave bolts loose.
2. Connect Throttle Sensor harness connector.
3. Start engine and warm up sufficiently.
4. Measure output voltage of Throttle Sensor using voltmeter.
5. Adjust by rotating Throttle Sensor body so that the output voltage is 0.45 - 0.55 volts.
6. Tighten mounting bolts.
7. Disconnect Throttle Sensor harness for a few seconds and then reconnect it.

With the locking tab of the connector pointing up and looking at the back of the connector as the wires from the wire harness go into it, terminal #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

Output voltage is measured across terminals #2 and #3 from the harness side of the connector.

A&W

Question:

Do you know the procedure for checking out the TPS and adjusting the idle?

Answer:

For the full blown check, it has a few steps involving the ECU and it's connections to the TPS. We're going to skip those, assuming they aren't a factor. Also, trying to describe which terminal on the ECU harness to check would be a nightmare w/o a diagram. This is hard enough as it is!

Checking for the correct voltage, ground circuit, and resistance are not that tough. So here ya' go...

POWER SUPPLY:

Disconnect the TPS harness and look at the terminal side of the connector. (this is the side with the terminal connectors in it) With the locking tab pointing UP, the terminals are A, B, and C, from left to right. (Confusing, huh?) This is measured from the male half of the connection that goes to the engine.

Turn the ignition ON and measure the voltage between terminal C and ground. It should be approx. 5v.

GROUND CIRCUIT:

Ignition OFF. Check for continuity between terminal A and ground. Continuity should exist.

RESISTANCE:

Make sure that resistance between terminal A and B of the connector half (female) that goes to the TPS changes when opening the Throttle Valve manually.

The results of the test should be:

Accelerator Pedal Condition Resistance in k Ohms

Completely released Approx. 2
Partially released 2 -10
Completely depressed Approx. 10
If test shows "No Good", replace Throttle Sensor.

VOLTAGE ADJUSTMENT:

1. Loosen the 2- bolts that hold the TPS.
2. Start engine and warm up sufficiently.
3. Measure output voltage of Throttle Sensor using voltmeter.
4. Adjust by rotating Throttle Sensor body so that the output voltage is 0.45 - 0.55 volts.
5. Tighten mounting bolts.
6. Disconnect Throttle Sensor harness for a few seconds and then reconnect it.

Note: With the locking tab of the connector pointing up and looking at the back of the female connector as the wires go into it, terminal #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

Output voltage is measured across terminals #2 and #3 from the harness side of the connector.

Adjusting the idle is pretty straight forward:

Disconnect the TPS harness and turn the idle adj. screw on the IAA to get the car to idle at 650 rpm. Reconnect the TPS harness and your beloved should purr at 700 or so rpm. (The Factory manual gives a +/- tolerance of 50 rpm.) The IAA is at the back of the intake manifold. You can see it standing over the right (passenger side for N.A.) fender and looking at the funky device with the dime size recess for the adj. screw.

Regards,

A&W

'91 s13

Answer 3

could be. I think the mechanic is right. a throttle position sensor could be the problem. but get a second opinion before you start replacing parts.

Answer 4

he probably told you right ,,but id take it to auto zone and have them scan it,,its free ,and they can tell you if it is the sensor,,there are two things that can cause this the throttle position sensor,,and also an 0-2 sensor will do this,id have it checked ,before i bought parts i didn't need,,you,ll save money doing it this way,,good luck hope this help,s.

Answer 5

I think you can tell who the real mechanic is here...(hint":its not the easy stuff) In my humble professional opinion, you need a professional diagnosis. If you knew how to fix it yourself, then you'd fix it yourself. most of these answers remind me of going to the doctors and asking the patients in the waiting room what they think you need because the doctor is too expensive.

Answer 6

i might initiate with marvel absorbers or struts, counting on your motor vehicle. if your motor vehicle has greater suitable than 60-seventy 5,000 miles this could be a stable beginning factor. Shocks and strut overall performance starts off to pass to pot after this mileage.

Answer 7

it sounds like you need a new throttle sensor.

Answer 8

I think that your friend is right but how high is "racing"? and how cold is it at your house when you start it? How long til it idles off?

Answer 9

Your mechanic friend is probably right.

Answer 10

your buddy sounds like he may be correct, but i would follow the advice of dodge man