Throttle Position Sensor on our cars?

[Svashtar]

Hey guys, I drive my MM only a few days a month now, so haven’t checked in for a long time (as usual, sorry!). I still have a lot of small jobs to get done on it and need to get off my butt and just do it, but generally it’s running pretty well.

Great to save gas at $4.20 gal, but also not good as problems can sneak up on you from it sitting.

Anyway, I think my car needs a new throttle position sensor, or whatever Ford calls it. I replaced one 6 months ago on a Hyundai that was doing exactly what my MM is doing now.

That is, driving cold only (with cruise control on for consistency, to take my foot out of the equation), while watching the ScanGauge report RPM about once every 2 seconds: 1750 - 1980 - 1875 - 1700 - 1810 - 1865 - 2000 - 1790, etc., etc. You can feel the car surging and falling off slightly each time. Jump on the freeway and take it to a consistent 2500 RPM for a few miles, and problem goes away, but as soon as you come to a full stop the engine can just die. Starts right away, dies again. After you coax it for a while it seems to run fine and idles OK without dying.

All this is intermittent. Oh, and while the RPM is surging, the MPG stops calculating, shows 9999 mpg while it’s trying to figure out what the engine is doing.

If there is such a sensor for our cars, please let me know and if you know where to find it on the engine. I searched RockAuto and don’t see a part with this specific name. “Speed sensor” maybe?

Thanks for any info!

Norm




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[Logan86]

Throttle position sensor is located on the throttle body and has two allen head bolts. Super easy to change out. My car was surging at idle with the AC running so I changed that out, the idle air control valve and cleaned the MAF. Problem is gone.

[Svashtar]

Throttle position sensor is located on the throttle body and has two allen head bolts. Super easy to change out. My car was surging at idle with the AC running so I changed that out, the idle air control valve and cleaned the MAF. Problem is gone.

Thanks Logan. I clean the MAF periodically when I oil the air filter. I’ll look for one at my LPS. Not sure what or where the idle control valve is, but I’ll ask for one of those as well.


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[Logan86]

It's right there next to the TPS so if you do them both at the same time you will be good.

[Svashtar]

It's right there next to the TPS so if you do them both at the same time you will be good.

Thanks Logan.


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[Svashtar]

It's right there next to the TPS so if you do them both at the same time you will be good.

I did the TPS and believe that fixed it, no more surging. I’ll keep an eye on it and also change the idle air control valve if it happens again.

Thanks again for the information Logan. [emoji1531]


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[Logan86]

No worries, I'm glad to see it worked out!

[Svashtar]

Yep, no more surging, but after a cold start and on the freeway at 2500 RPM for ten miles, then pull off the road and brake the engine dies immediately.

I went ahead and replaced the idle air control valve as well. That and the TPS seem to give up together. [emoji848][emoji6]


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[justbob]

Yep, no more surging, but after a cold start and on the freeway at 2500 RPM for ten miles, then pull off the road and brake the engine dies immediately.

I went ahead and replaced the idle air control valve as well. That and the TPS seem to give up together. [emoji848][emoji6]


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You can adjust the TPS to the optimal 0.98 setting for idle but as long as it is anywhere in the ballpark the PCM will adapt. If you got one that is way far out of range it would definitely cause a stall.

Just turn the ignition on but don’t start it. Back probe the middle TPS wire with a small pick and touch the red lead from a multimeter to it and ground the black. To adjust, loosen the two screws and twist the whole TPS in what ever direction you need relying on the slop in the holes.

Mine was around .50, so bad I just drilled the brass sleeves out to allow more adjustment.


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[Svashtar]

You can adjust the TPS to the optimal 0.98 setting for idle but as long as it is anywhere in the ballpark the PCM will adapt. If you got one that is way far out of range it would definitely cause a stall.

Just turn the ignition on but don’t start it. Back probe the middle TPS wire with a small pick and touch the red lead from a multimeter to it and ground the black. To adjust, loosen the two screws and twist the whole TPS in what ever direction you need relying on the slop in the holes.

Mine was around .50, so bad I just drilled the brass sleeves out to allow more adjustment.


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Thanks Bob, I didn’t realize it was adjustable. I just aligned mine the way I had to with the holes in the throttle body, which meant I had to turn it clockwise (downwards) a fraction against a little spring tension. I’ll try your tip and verify what I’m getting.

The car has been stalling in this manner (after starting cold and running smoothly at mid to high RPM for 10 minutes then coming to an abrupt stop and idle) since before I got the new TPS and idle air control valve, so after replacing the TPS I assumed it’s the air valve, but appreciate the info.


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[justbob]

The only other things that quickly come to mind in my tiny head that would cause those exact symptoms is weak line pressure in the trans causing torque converter issues. They can hang a bit when hot and stopping abruptly, and normally hit or miss or require just the right braking conditions to stall the engine.

A weak charging system can play hell once warmed up and definitely affect idle.

If your air or defrost is on and the tune doesn’t quite bump the idle up enough to accommodate it.

Fuel delivery, but normally that is more pronounced when WOT.




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[decipha]

just for the record there is no optimal closed throttle position voltage. People that claim .98 volts or 1 volts or xxx volts have no idea what they are talking about.

The ford ecu saves the lowest throttle position voltage it sees at key on as RATCH so long as it does not exceed RATIV. In most stock calibrations that means that as long as the closed throttle tps voltage is between 0.7 volts (min default tps volts) and 1.25 volts (RATIV) it is PERFECTLY WITHIN SPEC. There is nothing to be gained or lost by adjusting the throttle position sensor to reach any desired voltage its just lunacy and has absolutely no affect on anything.

If your rpm was surging while at steady throttle cruise then that would be most likely a misfire. Misfiring would most likely be an ignition fault more times than not. If this occurs after sitting a while its most likely burning some oil causing it. Its common for the 4v engines to have leaking valve seals and if worn enough will cause a substantial amount of oil to leak past after sitting for a couple weeks. Very common issue. If it subsides after driving it for a while then most likely its the valve seals.

[justbob]

just for the record there is no optimal closed throttle position voltage. People that claim .98 volts or 1 volts or xxx volts have no idea what they are talking about.

The ford ecu saves the lowest throttle position voltage it sees at key on as RATCH so long as it does not exceed RATIV. In most stock calibrations that means that as long as the closed throttle tps voltage is between 0.7 volts (min default tps volts) and 1.25 volts (RATIV) it is PERFECTLY WITHIN SPEC. There is nothing to be gained or lost by adjusting the throttle position sensor to reach any desired voltage its just lunacy and has absolutely no affect on anything.




You can adjust the TPS to the optimal 0.98 setting for idle but as long as it is ANYWHERE IN THE BALLPARK THE PCM WILL ADAPT. If you got one that is way far out of range it would definitely cause a stall.

Just turn the ignition on but don’t start it. Back probe the middle TPS wire with a small pick and touch the red lead from a multimeter to it and ground the black. To adjust, loosen the two screws and twist the whole TPS in what ever direction you need relying on the slop in the holes.

MINE WAS AROUND .50, so bad I just drilled the brass sleeves out to allow more adjustment.


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[decipha]

I didn't mean to offend I didn't quote you because I wasn't directing anything towards you.

I was simply stating that as long as the closed throttle tps voltage is between 0.7 and 1.25 volts its perfect and does not require any adjustment.

[Svashtar]

just for the record there is no optimal closed throttle position voltage. People that claim .98 volts or 1 volts or xxx volts have no idea what they are talking about.

The ford ecu saves the lowest throttle position voltage it sees at key on as RATCH so long as it does not exceed RATIV. In most stock calibrations that means that as long as the closed throttle tps voltage is between 0.7 volts (min default tps volts) and 1.25 volts (RATIV) it is PERFECTLY WITHIN SPEC. There is nothing to be gained or lost by adjusting the throttle position sensor to reach any desired voltage its just lunacy and has absolutely no affect on anything.

If your rpm was surging while at steady throttle cruise then that would be most likely a misfire. Misfiring would most likely be an ignition fault more times than not. If this occurs after sitting a while its most likely burning some oil causing it. Its common for the 4v engines to have leaking valve seals and if worn enough will cause a substantial amount of oil to leak past after sitting for a couple weeks. Very common issue. If it subsides after driving it for a while then most likely its the valve seals.

I appreciate the info, but as outlined in the OP, it doesn’t happen after sitting, and a misfire (and I know what that sounds and feels like), wouldn’t cause the RPM to go from 1680 to 2010 to 1950 to 1720 to 1830 and back again multiple times (as polled by the ScanGauge 30 times a minute) while running with cruise control on. Replacing the TPS fixed the surging completely. Even though I’m no mechanic, based on the exact same experience with another car, I kind of expected that frankly.

In any case if it were leaking valve seals I would see oil loss as it blew out the tailpipe, not to mention blue smoke, and after replacing the OF housing gasket it hasn’t lost a drop.

I replaced the idle air valve yesterday, but won’t repeat the conditions where it’s been stalling until this morning, so we’ll see.

Even that won’t be 100% definitive, because I’ve had to drive it with the stock tune (with 4:10 gears) for the past week to get it ready for it’s two year smog, which requires all tests to be passed to give a “no codes found, ready” condition. I hate to confuse the car that way, but the ABS has been out for repair anyway.

The acid test will be after I reflash it with Marty’s tune and repeat the same drive with the new IACV.


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