TPS voltage setting

SVT CAMR

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OK I returned the 98 cobra back to a street car. So for giggles I reset the the fuel pressure at 40 with the line off and capped.

Then I messed with the TPS Voltage and experienced surging at idle. Then I noticed the car would die when coming to a stop.

I thought it might have been the old super chip I put in but after a few days of driving there was still an issue with the surging and stalling.

I have also been trying to find that nice spot for clutch engagement.

I was under the assumption I should adjust the TPS Voltage with the car running. WRONG!

It needs to be adjusted to 0.98 volts with key on engine off. I did this and my idle dropped to about 700 rpm.

The car is real quiet at idle. So now the surging is gone and the stalling is gone like nothing ever happened.

Another huge thing I noticed is my take off in first gear was amazing and all of the sudden found my sweet spot. Amazing that 200-300 rpms made a difference with how my clutch reacted on take off. I always felt as if I was feathering it to properly take off. This feeling is gone.

Just thought I would throw this out there if anybody else is have any similar issues. I'm curious to see if my gas milage with improve with the lower idle too. This is what prompted the super chip change out in the first place.
 

Ferocious

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Just so everyone knows, the .98v setting for the TPS is just a myth. There is a range for tps voltage that the computer reads. If the voltage is out of that range, the sensor will throw a code. Just wanted to throw that out there.
 

ttocs

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I thought I read when you start the car it reads the TPS voltage and as long as its with in range, it calibrates that as the idle voltage?
 

SVT CAMR

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I thought I read when you start the car it reads the TPS voltage and as long as its with in range, it calibrates that as the idle voltage?

Yeah I heard the same stuff too but apparently it does not just adjust the rpm idle speed or I would have never needed to touch it in the second place.

I will throw this out there I was having charging issues so I bumped the idle up via the screw on the throttle body. I have a single blade FRPP. So earlier in the week I adjusted the TPS voltage with the idle screw. I still had the problem of surging and stalling. My car never did this before so I blamed it on the chip change.

Today I was like WTF! I gotta fix this. I just thought back to me being lazy and adjusting the screw on the throttle body and said to myself thats not the way you should have done it. So i looked at the screw and saw the spot where the lock-tite ended and put the screw back to there. Then I got a phillips screw driver and loosened the screws on the TPS. Adjusted from there with the car running. shut the car off then put key into the on position and saw my volts move from .98 to .99.

Now I pull out my useless Hayes manual and sure enough it say to adjust with the key on and car NOT running. I did this.

Went for a ride and BAM all fixed like it never happened. A complete 360. Now it won't even stumble with my foot on the brake pedal hard at a light after slowing down to a stop.

FWIW te Hayes book said .50 - 1.00 is where to set it. I say stick with .98 and call it good. Glad this is behind me I went for another ride and again not a problem at all. I love this time of the year any excuse to go for a ride. Oh sure honey I'll drop the kids off. :wave:

EDIT Before all this I started clocking the MAF to see if it would help the situation but it did nothing. Same thing with the AIC right next to it and no change either.
 

Ferocious

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I thought I read when you start the car it reads the TPS voltage and as long as its with in range, it calibrates that as the idle voltage?

As long as the voltage is between .6-1.1 the computer considers it acceptable and will take care of the rest.
People who 'set their voltage' should probably do a little more research on the ford tps as they are not adjustable.

http://www.veryuseful.com/mustang/tech/engine/Mustang-TPS-FAQ.html
http://mustangforums.com/forum/5-0l-1979-1995-mustang/306203-tps-voltage.html
 

SVT CAMR

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Just so everyone knows, the .98v setting for the TPS is just a myth. There is a range for tps voltage that the computer reads. If the voltage is out of that range, the sensor will throw a code. Just wanted to throw that out there.

All that means is it won't throw a code so long as your in the range. Does not mean your car won't idle like shit like mine did before.

The only time this needs a looking at is if there is a problem. If it's not broke don't fix it. If its working it would not hurt to document it in it's working state at what ever voltage it reads.
 

SVT CAMR

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As long as the voltage is between .6-1.1 the computer considers it acceptable and will take care of the rest.
People who 'set their voltage' should probably do a little more research on the ford tps as they are not adjustable.

http://www.veryuseful.com/mustang/tech/engine/Mustang-TPS-FAQ.html
http://mustangforums.com/forum/5-0l-1979-1995-mustang/306203-tps-voltage.html

all I know is I had a problem and now it is fixed. Just like that and the computer had nothing to do with it. You also have to keep in mind when there is a chip involved and other part installed it can change some of the rules. That my opinion anyway.
 

SVT CAMR

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Ok I read the article on the top link and I see where your coming from.

He did mention if the idle screw is set correctly. So yeah I put it back and set the TPS with in range.

I almost want to go set the TPS to a lower voltage and see what happens. No way I not touching now.

I just don't get it though. if I move the screw I move the blade and the voltage. if I move the TPS sensor I also move the blade and the voltage. So I really have no idea what it means to have the screw set properly. The blade will be open this much whether it is done with a screw or by moving the sensor. I'm just glad I lucked out.
 

5-oh-MUSTANG

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From what i know fox's have to have a properly set tps voltage or the car will have issues. And i also know for the 94-95, the ecu is so crap and delicate its better to have it around .98/.99 too. It doesn't hurt to try.
 

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