I am stumped here. I have two TPS sensors, and both are having the same problem. The one that I have been using is slotted, and I got the voltage down to .29v at idle/rest. It still registers at 100% throttle when I put the gas pedal down to the floor.

The problem is this, driving along is fine, but when you take your foot off the gas, the TPS still registers about 2%, so the car wont idle, cuz it thinks you still have your foot on the gas. But, when I blip the throttle, it will go to 0%. Very annoying. I thought it was the throttle blades were not closing all the way, so I put another spring on it to pull it back, but did absolutely nothing, so that is when I started datalogging it to figure out what was goin on here.

So, I swapped out the TPS sensor for another one I had laying around, unslotted. At rest it registered .70v. I didn't care, as its unimportant. I just wanted to see if it would go to 0% after you slowly pull you foot off the gas... so I tried it. Same damn thing. You have to forcefully blip the throttle to go back to the idle state, at 0% throttle.

So, I measured the shaft of the AS&M TB, and it was .156". I measured my stocker, and it was the exact same. So, what is causing the TPS sensor to not go back to 0% when you slowly pull your foot out of the gas, but if you forcefully blip it, then it will go to 0%??

I am very confused, and I want to get this fixed asap, cuz Im gearing up for another dyno day next saturday!

Thanks for any and all advice!

~Cody

 

FWIW, I stuck a screw driver in the end of both sensors, and the springs are still very strong that bring it back to its resting state. I cant figure out what would keep it from going back to 0% when you let off the gas slowly, but if you nail the throttle like your wanting to race or something, then it goes to zero. And two sensors do this, one slotted and one not.
No one has had this problem before??

 

If you mean the engine continues to rev when you let off the gas, mine is doing the same thing after I installed a ported tb and intake. I can't figure out what the heck is going on!!

 

Sounds to me like the throttle is sticking open slightly, not a TPS issue.

 

I know what you mean fastbird, but its not sticking. Its fully cleaned, and the spring is pretty strong on the return side. But, Like I said, I added another return spring from an old carburator, and even with that attached, its still doin it. So, That leads me to believe that the tb is going back to its resting state when I let off the gas, but the sensor is not. Im stumped.

 

And yeah, it does continue to rev, but not because of a vacuum leak. Mine continues to rev because when I have my laptop hooked up, the tps sensor is still reading that my foot is on the gas. once I stab the throttle, it then finally goes back to 0% throttle.

 

The TPS sensor has to move with the throttle shaft.... the only possible explanation for them not moving together would be that the hole in the TPS sensor is oversize, leaving it loose on the shaft. But you've already indidated the spring in the TPS is healthy, and that would cause even a loose connection to the shaft to allow the sensor return to its "rest" position. I doubt its the TPS.

Have you looked at the throttle bores for evidence of the blades contacting the bores and getting stuck?

 

Exellent procession through the rationale of how it works, and I did the same...

Yup, I checked the bores of the TB, no evidence of it hanging up there either.

What else is there to look at Fred? I am stumped here.

The only thing I can think of is a fellow tuner friend said to put the IAC at about 20 counts at high idle. So I did. I used the set screw to open up the blades slightly.
I have since read that it should be 25-30 counts. I am thinkin that if I pull some screw out of it, and make the IAC work more, that somehow this could go away??
At this point its worth a shot.

What is your best guess at IAC counts, and TPS voltage at hot idle Fred?? Maybe you can set some things straight here.

 

I can only tell you what a stocker runs on TPS voltage (0.67) and IAC counts (20-40). My stroker is a mixed bag, with the engine running on an aftermarket ECU, except for the IAC motor, which is still running on the stock PCM. IAC counts can get pretty close to "0" at times, but it never bottoms out completely. TPS voltage on my setup is not critical, since the MoTeC accepts the closed throttle and open throttle voltages and uses them as the 0% and 100% points. TPS is about 0.70V.

 

hmm, ok, thanks Fred.
On a side note, I think I figured out what was wrong with my faulty tps readings.
The plastic end that the throttle cable connects to was loose on the shaft. So I took the TB off again, and sure enough, when I took the bolt out that holds the plastic plate to the shaft, the thing was butchered! So, the plastic plate would move a little on the shaft, then the shaft would move, thereby creating a new idle position when I let off the throttle. I wish I could remember who I bought this used AS&M TB from, cuz I would fly to their house and personally punch them in the damn face. It seems all my problems stem from a effed over TB. So now I have called AS&M, and I have a new shaft, plastic throttle peice, spring retainer, and stop arm orgered, at a cost of 130. I hope I can get it all squared away before saturday for the dyno, cuz I really want to do a damn money pull on my fireturd.

If it wasn't for bad luck, I would have no luck at all.

 

Well, update time. I got all the parts to rebuild the throttle body, and guess what?? No more stupid TPS issues. Funny how 130 dollars later they disappear!

So, now that I have that cleared up, its time to load in some new programs... (thanks Chris!) and do some datamaster loggin to get this beast on track for Rippies Dyno day! Woot Woot!