TPS voltage out of wack on TBI

[steveno]

I had a problem posted before and seemed to have resolved the issue, this might be related or not to other previous issue. 79' AMC 258 i6 / 4.2l in 84CJ7 with gm 4.3l TBI with spark control. Jeeps starts fine idles around 1100 for 8 seconds then drops to about 700 to 800. A second after it drops the cel light comes on. I do the paperclip and get a code of 21. High voltage for more than 8 seconds and >15pounds vaccum at manifold. I did the three tests on the tps, First test power from ECM is 12.1 volts (range is 11 to 12 volts.) 2nd test for ground 12.7 volts (range is 11 to 12 volts) 3rd test is 4.88 volts closed throttle 4.92 at open throttle. (range is .5 to .9 closed and 4.5 to 4.9 open throttle.) So the starting range is way high and that makes sense that it idles high. Could there be a open ground? 12.7 is higher than range or that doesn't matter. The real problem is the starting voltage which is way too high, Bad TPS? Bad ECM but ECM is giving correct 5 volts to start with and if the ground is good at 12.7 then the TPS is feeding a high voltage to the ECM and idles high for 8 seconds and then drops once the 2.6 volt default kicks in, which is still high and it idles a little high still. Which makes sense and seems that the ECM is working as it should be. So I'm thinking bad TPS or bad Ground, not good with electric so my question is 12.7 volts ground on TPS ok? if so then thinking bad TPS. IF not then possible open circuit ground?
Thanks. Hope your as confused as me....

 

[Scooter402]

IMHO, all signs point toward a bad TPS, especially if you're only getting .04 variation in voltage from closed to open throttle. Given that there should be 4-5 volts from closed to open, I'd say the sensor has gone kaput. Not unheard of, I had to change out the TPS on a TPI setup I had on my 383 stroker. It was doing almost exactly the same thing.

 

[steveno]

I changed out the TPS, after riding and letting computer learn again. Seems to be working great, just have to get out for a decent ride and see if it holds up.