TPS voltage settings

Ryan A Harris

Registered User
I have just swapped on a 75mm T-body onto my 95 SC. I have a really high idle now.

I 1st had the butterfly stop adjusted so the butterfly is not closed, and started with the bleeder srcew all the way down. The car still idled high. We next looked at the volage of the TPS, it was out, so we set it. Idle was still high. So I pulled the plug on the IAC, and nothing happened. I have purchased a new IAC and installed it last night with no change. So I pulled codes. I got 121, which was telling my tps is not in the propper working voltage.

My question is how do you set the voltage for the TPS? The way I had did was with the T-body in my hands, but the TPS plugged in measured the voltage. I had it set for .92v with the butterfly closed, and at .95 with the butterfly open. Did I do this correct?

This happened at the same time as new plugs went in. Nothing else was changed. I have no vac leaks, I looked for them last night, well the one I found I fixed(damn collar nut).

Thanks.
 
I check my tps by having the key on and the butterfly closed. I keep the tps loose so I can move it around and once I get it at .9 i tighten it down. I also had to elongate the holes on my tps to get enough movement out of it.
 
.95 with the butterfly open sounds low. I think the TPS might not be working properly. Don't go by the book for setting the position. I liked it around .92 at idle - seemed to give better off-idle throttle response. The computer shouldn't complain as low as .85V, though. Open butterfly on a 5.0HO can be up to 1.46V. I have also nearly always had to elongate the slots on TPSs
 
Ok, I have set the TPS to .94v, still has high idle. Then we did the Dr.Fred idle set. I don't even have a low enoguh idle to follow his step. My car, no matter what idles at 950 at the lowest. No other codes are present.

The throttle body is the 75mm "preformance products" one for a mustang, it was on the car before, with no trouble at all. I know of a few guys in the SCCoO that have the same T-body on their car with no troubles at all. I'm thinking of swapping back on the stocker T-body, but I don't see how that will help. The T-body has a "adjustable" TPS on it. The TPS bolts to a plate that can be lossened and rotated to help adjust the voltage.

Other problems with the car at this piont are as follows:

1. Possible broken cats, for the 2nd time in about a month
2. EGR tube has a small hole in it. Its been ther for ever.
3. Small leak on the rad, again, just found that last night.


The spark plugs were changed at the same time as the T-body. Nothing else was done at that time. We have searched for vac leaks, and none are found.

EDIT: 214 is now being pulled. Like I said the plugs had just been changed. But I don't see any of the symptoms that come with a 214 code. Car does not have a low, or rough idle. We're going to have a look at the plugs and wires now.
 
Last edited:
Ryan A Harris said:
Ok, I have set the TPS to .94v, still has high idle. Then we did the Dr.Fred idle set. I don't even have a low enoguh idle to follow his step. My car, no matter what idles at 950 at the lowest. No other codes are present.
If you can't get the car to idle lower than 950 then you have an air leak. Plain and simple. With the IAC disconnected and the throttle blade closed completely the car should quit or at least idle down to like 400rpm. Re-check your PCV or other places for a possible leak.
 
Dave, we had spend 3 hours looking for any sort of a leak, we came up empty. Aside from the EGR leak that I know I have, and was there beofer the T-body swapped on. I think the problem may lie within the throttl body bleeder screw. Its all the way down, and still idles high. I'm going to swap on the stock T-body on friday. I'm also going to try out a longer screw for teh thottle stop screw. Did I mention that the car ran find until this T-body was bolted on. Before I left the shop, the only code that was being pulled was a 411(I think it was that). That codes is saying high idle. Code 214 was emliminated by cleaning the cam sensor out a little.

Thanks for replys thus far.
 
Did you install the plastic spacer (dust cap) between the TPS and throttle body?
On the BBK TB, the spacer is too wide and causes the TPS to bind. Remove the
spacer or cut it down. You can check the TPS voltage (min and max) with car KOEO to verify if it's sticking or not.
 
I do not remeber at this point if the "dust cap" was installed or not. I'll be romving the T-body on friday to compare it to the stock unit, so I'll check then. Thanks for that, it maybe it.
 
Ryan, I've heard of air leaking past the threads on the Bleeder Screw.
Fix was some teflon tape, worth a quick try.
 
Steve, I had originally had telon tape on that screw when it was 1st installed. I'm thinking that something is wrong with the bleeder screw desgin. Both with the hole and the screw its self.
 
I think you may be onto something Ryan. With all the machining screwups I've caught on Edelbrock stuff lately it would not surprise me one little bit.
I'll pull my bleeder screw and have a look at it. I've not pulled that screw out yet but it should have an Oring setup to seal it off. The comment made earlier about using Teflon tape on the threads to seal it tends to make think there's no Oring. I'll have a look.
 
When i put my tb on it idled high then lowered after the car stopped and dropped idle after 3 sec. The fix was to unhook the battery and wait for 10 min then hook the battery back up.It was fine then.
 
Ok, I have found my troubles. Dave was right, it was an air leak.

It was the butterfly. The butterfly is under size compared to the bore. So its letting air go by it when the adjuster is fully closed. The stock TB is on, and the car is fine. So I guess I have to make up a new PROPPER butterfly now.

Thanks for all your time and help.
 
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