forum, My check engine light just came on. I did the ole paperclip trick and it looks like a CODE 21. Fuel Injection Throttel position sensor (signal voltage high). MY IDLE DOES IDLE HIGH most of the time.. 1200-1300 rpm. CAR runs super fine.
I am NOT VERY MECHANICALLY INCLINED.
is there anything I can do, relatively EASY to fix? or to check and see if it is a code 21?
If I have to check something, where do I find it? (ie. the throttle position sensor).
thanks in ADVANCE for any and all your help! Bob

 

Throttle Position Sensor is bolted to the right side of the Throttle Body and is mechanically linked to the throttle butterfly. It has a 3 wire harness - generally gray, blue and black. The ECM sends 5 volts to it on the gray wire, and anywhere from about a half volt (idle) to more than 4 volts (Wide Open Throttle) is returned to the ECM on the blue wire. This voltage is generated and is directly proportional to the position of the butterfly which is controlled by the accelerator cable (a wiper inside of the sensor essentially loses resistance as the throttle is opened increasing the voltage return). The black wire is ground and is shared with two other Sensors: Coolant and Air Temperature. If there was a problem with that ground circuit, you would or should have codes for those Sensors. The Code 21 means that it's seeing an impossible, high voltage for everything else that's going on. And since the Gray wire carries the full voltage potential for any throttle position, that voltage must somehow be getting to the Blue Wire. That leaves three possibilities: the harness has chafed and rubbed a couple of holes in the wires so they are now touching or 2, the terminals inside of the connector are touching or 3, the TPS has failed internally. It's fairly easy to troubleshoot the first two - disconnect the harness and see if it goes away - if so, that should generate a new Code or 22 which means there's no signal at all from the TPS (and there shouldn't be if it's disconnected because that opens up the circuit). If it does, replace the TPS. If it doesn't, you're going to have examine the wiring and connector to find out where the wires are making contact. Let us know what you find - there's a specific procedure for replacement and you'll need a DVM to complete the job.

 

Cod2 21 is set if:
1-TPS voltage is >2.5Vdc
2-Engine is running
3-air flow is <15gm/sec
-all three conditions are met for >3sec

If you are going to measure TPS (Throttle Position Sensor) voltages I would suggest buy one of the breakout harnesses that plugs in between the TPS and its cable to bring out all the wires to facitilate easy hook up of test equipment.

You can pick up a nice DMM and some jumper wires at Radio Shack, along with the above connector is about all you need to tackle this problem. Well that and this Forum of course...

 

http://members.shaw.ca/corvette86/Code%2021.pdf

 

thanks to maxwell smart, 65z01 and SunCr.. any more thoughts keep em' coming! thanks

 

I posted this on your other thread.

http://forums.corvetteforum.com/show....php?t=2025563

 

Checked volts were 2 idle 4 wide open. Idling usually about 1200-1300 rpm. Changed TPS and PRESTO! idle down to 600-700 and NO CHECK ENGINE LIGHT! NO FAULTS!!!! YEEE HAAAA..... it was actually a pretty dang easy fix. thanks to everyone for help. Bob in Mich

 

I have a 1985 corvette and can't bring the idle down under 1200. I just put a new battery and tps but did not fix it.
Amy suggestions?
Thanks

 

Here's a link for the correct idle setting for TPI cars.
https://www.corvetteforum.com/techti...D=55&TopicID=2