Hoping you all could steer me in the right direction...

1981 Corvette Automatic. Mechanically 100% stock. Historically, had TPS sensor disconnected. Drove great other than running very rich and poor MPG and check engine light 23. Recently tested TPS and ended up replacing it, as it had failed. Followed all steps in service manual precisely.
New TPS installed will all equipment hooked up accordingly along with new air horn gasket/etc. Adjusted via adjustment screw to 0.56v with key on (not running) and at idle position after install.

Issue: car now starts/runs/shifts perfectly when cold (first 5-6 minutes of driving). Once it warms up and idles down, car then shifts incorrectly (shifts too soon/etc) and idles poorly.
Completed troubleshooting so far Includes: TPS adjustment (0.56v) and spans up to 4.3v full throttle position, ECM checked and working properly, M/C solenoid checked and working properly, O2 sensor checked and working properly, all vacuum lines connected, etc. I disconnected battery over night to try a reset. Also drove it 20 + miles. Still no change. No check engine lights/codes...

Now, if I disconnect the new TPS, the car goes back into running rich with poor MPG but idles and drives perfectly just like it did with the old "failed" TPS.

I am baffled that all seems to run perfectly with the new TPS when cold (idles great, no misses, shifts perfectly, doesn't run rich--best its ever run!), but as soon as it warms up, the above symptoms occur.
Any advice would be greatly appreciated. Thanks in advance for your time and expertise. Excited to officially become part of the CorvetteForum! Thanks all!

 

I hate to say this, but I would check for vacuum leaks. I begin by disconnecting and plugging all non-essential vacuum hoses (headlights, brakes, etc.)

 

Thanks itsforfun. I will check

 

The "too soon shifting" is a real pain for drive-ability.

What I did was put a very small toggle switch in my center console, right under the parking brake lever. I intercepted the transmission lock up harness, and broke one wire to each side of this switch.

So now I choose when the transmission can go into full lock up, not the ecm. Around town and non highway driving, no lock up. So much nicer to drive without the trans up shifting so quickly at low rpm's!! If I will be on the highway at speed for miles, then I flip the switch and it goes into lockup, drops the rpm's and better fuel economy. Turn the switch off as you come off the highway.

 

Thanks maxmachz. Interesting fix. Hmmm

Well after some more research I have confirmed that the ECM does not engage until after warm-up, which helps explain why there is such a difference of transmission responses between cold running and warm running. Basically, once the ECM is in control of transmission, all is goofed up

So my new question is, if TPS is new (and working), TPS adjusted to 0.56v at idle (key on) and runs up to 4.3v at full throttle position, M/C solenoid is working, O2 sensor working, can't seem to find any vacuum leaks, etc... what would your next step be? Could it be the modulator that is bolted to the transmission?

Lastly, does anyone have the name or link to the official tool that is used to adjust the TPS sensor (through the very small hole "double D" tip)? I can't seem to find it online

Thanks again all!

 

Hey, I ve been trying to remember cc carbs from when i had an 82 z-28.
if i remember correctly, it takes a certain engine temp for the cc to go into closed loop (i think that is correct, it may be open loop) but anyway. i am thinking you may have a stuck/ leaking egr valve.
you say when the tps is dis-connected, it runs pig rich, but good, and with the tps connected, it idles and shifts poorly. I believe that when the tps is connected, the cc leans out after the engine reaches temperature and with a leaking egr, it would idle poorly, but with the tps dis-connected, it covers up the egr with the extra fuel being dumped in.
I may be wrong on this, cause usually when there is a vacuum leak, the engine will idle at an elevated rpm.
You may want to go to thirdgen.org and ask around, there were a butt-load of camaros with the cc carb.
Good luck, hoe it helps.
Jeff

 

Thanks Jeff. I will take your advice and look around and double check vacuum lines and EGR valve. Appreciate the direction