Question about 1997 Pontiac Grand Am

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98 grand am po121 replaced tps 3 times. new tune up, aic valve. when i clear code idle goes up from 600 to bout 1000. also affecting shifting

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  • bornagain1 May 01, 2010

    checked with tester car off 1.25v wot 5v car should be running? .5 v only? whats wrong if at 1.25?

  • bornagain1 May 01, 2010

    waiting on answer

  • toneman2121
    toneman2121 May 11, 2010

    i don't have much experience with throttle by wire. the system may need to relearn the parameters. either by a scan tool or manual. read more here.http://www.aa1car.com/library/throttle-b...

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  • Pontiac Master
  • 1,851 Answers

Your safest bet at this time is to take down the vin - call the dealer and ask about Service bulletins or recalls. I know this isn't what you want to hear most likely but we all have to have the factory from time to time.

Posted on May 01, 2010

  • Gary Rice
    Gary Rice May 05, 2010

    Please vote me helpful for effort here as it will enhance my life.
    Thanks from the whole family.



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  • Pontiac Master
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OBD-II Trouble Code Technical Description
P0121 - Throttle Position Sensor/Switch A Circuit Range/Performance Problem

What does that mean?
The Throttle position sensor is a potentiometer that measures the amount of throttle opening. As the throttle is opened, the reading (measured in volts) goes up. The powertrain control module (PCM) supplies a 5 Volt reference signal to the throttle position sensor (TPS) and usually a ground also. A general measurement is: at idle = .5 Volts; full throttle = 4.5 Volts. If the PCM detects that the throttle angle is greater or less than it should be for a specific RPM, it will set this code


Potential Symptoms
Symptoms of a P0121 trouble code could include:
* Malfunction Indicator Lamp (MIL) illumination (Check Engine Light or Service Engine Soon light)
* Intermittent stumble on acceleration or deceleration
* Blows black smoke on acceleration
* No start


Causes
A code P0121 may mean that one or more of the following has happened:

* TPS has intermittent open or short internally
* Harness is rubbing and causing an open or short in the wiring
* Bad connection at the TPS
* Bad PCM (less likely)
* Water or corrosion in connector or sensor


Possible Solutions
1. If you have access to a scan tool, see what the idle and WOT (wide open throttle) readings are for the TPS. Check if they're close to the specifications mentioned above. If not, then replace the TPS and re-check.

2. Check for an intermittent open or short in the TPS signal. To do that, you can't use a scan tool. You'll need an oscilliscope. The reason is because scan tools take samplings of many different readings over just one or two data lines and can miss an intermittent drop out. Hook up your oscilliscope and watch the signal. It should sweep up and down smoothly with no drop outs or spikes.

3. If no problems were noticed, perform a wiggle test. Do this by wiggling the connector and harness while watching the pattern. Does it drop out? If so, replace TPS and re-check.

4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts.

5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair.

6. Look for any water in the connector and replace TPS as necessary.


I suggest re-check or re-install your device; any bad connection can be the problem. Try it and tell us news.

Posted on May 01, 2010

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