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Old 01-21-2007, 03:34 PM   #1
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Question how can you tell if throttle position sensor is bad

i have set my tps at .90 and still having trouble in high rpm range. replaced plugs, wires,cap, rotor, fuel pump and filter, coil, and distib. car feels like it wants to cut out when i accelerate hard. at a lost here could use some info
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Old 01-22-2007, 12:15 AM   #2
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I've read that if you unplug it and the engine runs the same, that's a bad tps.

You could also check that your voltage increases with increased throttle position.

Maybe you're electronically pegging your mass air?
Check out the mass air tech article on www.lasotaracing.com for
a good technical yet understandable explanation of what that is
and how it affects how your motor runs
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Old 01-22-2007, 03:23 AM   #3
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get a digital volt meter and test your TPS.

with the ignition switch on, take the meter and probe the orange wire with the pos lead, and the black wire with the neg lead. you should have 4.9 - 5.0volts.

then probe the green wire and the black wire. that reading should be in the area of .90 volts ( as long as it is under 1volt you are fine)

then while still probing the green and black TPS wires, manually open the Throttle body sssslowly and watch the volt meter. The voltage should increase slowly and steady all the way to 4.9 - 5.0 volts at WOT. If it doesn't show a gradual increase then it is bad.

also, pull your codes.
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Old 01-22-2007, 03:24 AM   #4
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sounds like a fuel problem.

have you cleaned the MAF element?
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Old 01-22-2007, 03:29 AM   #5
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Did you use plat plugs?

I agree that there are a zillion things that can cause a high speed misfire (on the fuel and ignition side). More diagnostics might be in order.

Good luck.
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Old 01-22-2007, 11:29 PM   #6
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run a KOEO (Key On Engine Off) test. and if it throws engine code 52-53 (can't remember which one it is) it means your TPS is out of range...

That is how I found out mine was bad.
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Old 01-24-2007, 09:02 PM   #7
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i have replaced my tps and still having problem. what should be the proper fuel pressure. before i changed the pump and regulator i was running 32 psi at idle. also how would i check the injectors if needed. i put autolight plugs #25. and i have cleaned the massair flow sensor. ihave even checked the salt and pepper shakers onthe back of the intake they look pretty clean no corrosion. still lost H.E.L.P

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Old 01-25-2007, 12:25 AM   #8
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What codes did you see? This stuff is complex enough that we might as well use the tools available (self diagnostics).

FWIW, FP is ~38-39 PSIG with the vac line to the FPR removed and plugged. Anything over 30 PSIG at idle is fine.

You should see a lean code if the injectors are holding you up.

Good luck.
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Old 01-25-2007, 02:14 AM   #9
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does your car miss under WOT only while driving or will it miss in neutral if you give it WOT?

if it is only while driving, i'll bet your fuel pressure regulator is shot.
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Old 01-26-2007, 08:50 PM   #10
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the car will miss in neutral and while driving. i will have to go and get the codes i do not have the tool for that. how about the WOT relay? would that cause this kind of problem or would it just fail completely. someone also told me there is two fuses for the ECU if that is true where are they because i can not find them. was he full of ****.
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Old 01-27-2007, 12:44 AM   #11
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WOT relay has nothing to do with any of this.

What year of stang are we talkin here (and apologies if I missed it earlier). That will help us with assisting with codes and fuse lay-out.

Good luck.
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Old 01-27-2007, 02:05 PM   #12
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the year is an 89. i tried to pull the codes by a volt meter though the plug but that don't work. someone said there is a way to pull codes by the check engine light by it blinking. wondering if you know how.
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Old 01-27-2007, 02:32 PM   #13
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Quote:
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the year is an 89. i tried to pull the codes by a volt meter though the plug but that don't work. someone said there is a way to pull codes by the check engine light by it blinking. wondering if you know how.
check out this link - How to Check for Codes
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Old 02-10-2007, 11:16 PM   #14
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I have a very similiar problem but mine is perfectly fine under load but only at Idle it wants to die and not hold a steady idle. It will only do it under a Idle and very very very slight throttle applications. I have tested every aspect of the car and even gone to as far as replacing the MAF,IAC,Dist,plugs,wires,I am at a lose at what to do
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Old 02-11-2007, 12:16 AM   #15
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Why are you setting it at .90? Just wondering because I have mine set at .97 with the key on and the engine off. I had a problem with my car when I first put the engine back in it and the tps had to be set at .97 volts with the key on engine off. I say try setting it at .97 volts and see what happens. And as said previously make sure that when you operate the throttle slowly you see a gradual increase all the way to 4.9 or 5 volts.
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Old 02-11-2007, 02:56 PM   #16
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If you unplug the TPS and it idles up a little bit i would say to about 1000 RPM'S and then stays there and does not have the loping idle as it did when it was plugged in... would that mean that the problem is the TPS????
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Old 02-12-2007, 02:42 AM   #17
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Old 02-12-2007, 04:01 AM   #18
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95convgt, re-read post #3 and that will tell you if the TPS is bad.

and NO, the scenario you describe above doesn't sound like a bad TPS to me. The only way to be sure though is to test it.

and pull your codes, maybe the problem you have is elsewhere and this will give you a good start if there is a code stored.
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Old 02-12-2007, 12:57 PM   #19
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I have done all that. Thats why i stated that. I have tested every electrical item on that car. I even had 2 more Mech go over i used to work with. They couldn't find anything. We have tried to use a Voltmeter on everything including the ground wire connecter near the batt. Everything has been tested. Thats why i think it was the TPS. It registered between .8-1.0 on then it shows between a 4.5 and 5.0. There are no codes. We have KOEO and the KOER test both have come back with nothing. I am at a standstill.
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Old 02-13-2007, 02:38 AM   #20
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have you checked for vac. leaks?

also, is your car completely stock? what has been changed?
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Old 02-13-2007, 04:02 AM   #21
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have you checked for vac. leaks?

also, is your car completely stock? what has been changed?
First off i am sorry for all the punction issues. I had to get it all out while i remembered it. Thanks


yes i have and 2 other people have too...... I probably have gone through 3 or 4 cans or carb and choke cleaner to try and find a vacumn leak. Also when it is hooked up it draws a good vacumn. It acts like a lean Misfire when you are hardly on the throttle i mean ever ever so slightly. But you get on it. It won't mis at all. It runs like a bat out of Hell when you get on it WOT or even half way. It's puzzling to me i am almost at the point to take it to Ford and have them see what they can find just suck it up and pay the $85 they want for a Diag.

yeah it's completely stock besides running no mufflers. Still has the 4 cats though on it. I have checked the timing to check i dunno how many times to make sure it's at 10 deg

Crazy thing is whatever is causing it. Causes it to ping unless i use 93 Octane.


Things that have been changed are,plugs,wires,dist cap, dist, HAS inside dist, coil,IAC, MAF, EGR has been checked for vacumn on the exhaust side,fuel pressure is 28 while running 32 on. fuel filter, tps has been checked for voltage so has the small ground wire below the batt, o2 sensors, iac voltage, maf voltage everything. I am really at a loss. Thats why i thought it was the TPS. Cause when i unplugged it it held a idle perfect just a little high. I was told there is a small needle inside the TPS that can wear and cause it to get i guess you would say stuck. like in a valley, so thats why i thought that. My only other option would be to try the Comp to see if thats bad.
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Old 02-13-2007, 04:03 AM   #22
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Crazy thing is this all started to happen when i first tried to turn up my timing to 14*deg. I wonder if a sensor malfunctioned??? or got damaged
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Old 02-13-2007, 05:08 AM   #23
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Quote:
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Things that have been changed are,plugs,wires,dist cap, dist, HAS inside dist, coil,IAC, MAF, EGR has been checked for vacumn on the exhaust side,fuel pressure is 28 while running 32 on. fuel filter, tps has been checked for voltage so has the small ground wire below the batt, o2 sensors, iac voltage, maf voltage everything. I am really at a loss. Thats why i thought it was the TPS. Cause when i unplugged it it held a idle perfect just a little high. I was told there is a small needle inside the TPS that can wear and cause it to get i guess you would say stuck. like in a valley, so thats why i thought that. My only other option would be to try the Comp to see if thats bad.
You should have paid the $85 diagnostic fee at the Ford dealer before you threw all those parts at it. Sounds like you have done all you can, I say take it in.
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Old 02-14-2007, 04:27 AM   #24
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your fuel pressure should be at 39PSI, vac. line off at idle.

if it isn't, then you indeed have a "lean pop" issue.
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Old 02-14-2007, 04:40 AM   #25
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your low fuel pressure could be caused from a clogged fuel filter, bad fuel pressure regulator, or a faulty fuel pump....

unless you have an adjustable regulator and turned it down that low, in which case you need to turn up the pressure.
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Old 02-14-2007, 10:28 AM   #26
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So what should i try first a ADJ FPR. I plan on adding mods soon anyway. Fuel Filters are cheap i don't mind changing it. Then if it doesn't get any better new pump????
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Old 02-14-2007, 10:29 AM   #27
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Quote:
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You should have paid the $85 diagnostic fee at the Ford dealer before you threw all those parts at it. Sounds like you have done all you can, I say take it in.
Well it was a work in progress. It was all part of my Tune up since i really hadn't done all that much since we got the car and 99% of the parts i didn't pay for anyway.
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Old 02-14-2007, 11:44 AM   #28
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My car thre a code TPS semsor low circuit. I replaced the tps sensor and it still would throw a code and run like crap. I changed IAC valve cleaned maf, I was getting angry and could not figure it out. I got dynoed lastnight nad we figured it out. the plug that plugs into the tps sensor was bad and he fixed it. Now my car runs like new.
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