I've been having an on and off issue with very high idle - around 3000+ RPM. Usually if I shut the car off and restart, it will idle normally. I picked up a device called a C-Recorder to see if I can capture what's going on. Here's what it told me:

* P0122 Throttle/Pedal Position Sensor/Switch A Circuit Low
* P0650 Malfunction Indicator Lamp (MIL) Control Circuit
P0122 Throttle/Pedal Position Sensor/Switch A Circuit Low
P0650 Malfunction Indicator Lamp (MIL) Control Circuit
----( END )----

[font=Courier New]DTC: P0122 Throttle/Pedal Position Sensor/Switch A Circuit Low
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01. Fuel system 1 status ............................................ OL
02. Fuel system 2 status ............................................ --
03. Calculated LOAD Value ........................................... 0 %
04. Engine Coolant Temperature ...................................... 67 degC
05. Short Term Fuel Trim - Bank 1 ................................... 0 %
06. Long Term Fuel Trim - Bank 1 .................................... 8.59 %
07. Intake Manifold Absolute Pressure ............................... 101 Kpa
08. Engine RPM ...................................................... 0 Rpm
09. Vehicle Speed Sensor ............................................ 0 Km/H
10. Air Flow Rate from Mass Air Flow Sensor ......................... 1.61 g/s
11. Absolute Throttle Position ...................................... 0 %[/font]

Anybody see anything and/or have any advice that will point me in the right direction?

I'm no good at reading the data but first of all, It would help some if we knew what engine it is. Either way, I would look at removing and cleaning the Throttle position sensor and if that doesn't make a difference, replace it. Remember to unhook the battery for a bit to reset the codes after you try either of these things and before you try to check codes again.
Good luck,

Steve

It's a 3800sc, just swapped in this summer. Running an F23 5 speed. Still playing around with this new program to see if it will some up with anything of value, but here's a shot from when the idle was running high

Could be a bad TPS, the check engine light codes will show up some times because the PCM does not like the resistance of the Fiero bulb and usually never puts a check engine light on for that. Double check for the 5 volt reference on the grey wire at the TPS as the TPS uses this along with a ref ground not chassis ground to operate. I have also seen a weak or stick IAC cause idle problems as well but they do not throw TPS codes. Dan

Not 100% sure on the procedure to test the TPS. Found a couple of YouTube videos but none were Fiero specific. I'll give it a shot and failing that I'll look at replacing it. Looks like I can get one at Rock Auto for about $35.

All standard GM Throttle Position Sensors have 3 wires going to them. Typical wire colors are Grey, Black, and Blue.

The grey wire is the 5 volt reference supply from the PCM and this wire should have 5 volts on it at all times when the key is on.

The black wire is the ground supply from the PCM and this wire should be grounded at all times.

The blue wire is the signal wire from the TPS to the PCM. The voltage on this wire varies from about 0.50 volts or so at closed throttle to about 4 volts or so at wide open throttle.

If you are careful, you can push a needle or pin into the back of the TPS plug (while it is still plugged into the sensor) between the wire and the silicone seal and push it in far enough that it makes contact with the wiring terminal inside - this will allow you to test the voltage on these circuits while the TPS is still plugged in. Take care not to pierce the insulation on the wire or tear the silicone seal because if water gets into this connector, it can corrode the connections causing a failure.

I bet you are going to find either your TPS is not getting 5 volts on the grey wire or the sensor itself is bad and there is no voltage output on the blue wire - either of which condition can set the TPS code you are getting.

-ryan

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OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

So push a pin into the area on the grey wire, attach the red lead of a mulitmeter (20mA setting), and there should be 5 volts with the key on? Do I need to attach the ground wire to a good ground?

[This message has been edited by NetCam (edited 12-18-2013).]

I fired up the car today and ran it for about 15 minutes. I had to get it out into the driveway due to melting ice running into the garage. I figured I may as well kill 2 birds with one stone and let it warm up fully and capture some data while I was at it. I hooked up the recorder and just to see what was going on, I revved the engine just before shutting it off. As you can see from the graph, the absolute throttle position never changed - if this were an EEG, the patient would be dead, so now I guess either my TPS is shot, or I have a wiring issue with it.

[This message has been edited by NetCam (edited 01-12-2014).]

i think your on the money, TPS sensor or wiring, I personally would throw a TPS sensor at it and assume the wiring is good.

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1986 SE 3800SC/4t65eHD (12.871@104.96)
HX-40, FrozenBoost I/C, 80lb injectors & E85 Coming soon.....

Key on - Scanner connected and running - Engine Off.

Unplug the TPS and insert a u shaped paperclip between the Gray wire and the Blue wire of the harness side of the TPS connector. If the scanner than jumps to report 5V on the TPS, your TPS is bad.

If the scanner sits and does nothing - do this again with the key on - engine off - scanner scanning. Take a straightened paperclip and connect the blue wire of the TPS connector to the Tan wire of the IAT/MAT connector. If the scanner now reports 5v (ish) on the TPS the Gray wire is the bad one. If the scanner still reports 0 then the Blue one is the bad one.

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Also you should hook up your check engine (MIL) light.

[This message has been edited by phonedawgz (edited 01-12-2014).]