Throttle Position Sensor voltage out of range

[RustyDusty]

Hey my 1987 ford ranger with the 2.9 has a few issues that I've been trying to track down. It likes to die right after I start it. Idle is a bit sporadic, goes up and down and up and down, sort of like a pendulum. It also likes to die when I take it out of park and put it into gear whether its Drive or Reverse. After I start it up again it will usually go into gear without dying, it just likes to die the first time around. I checked the codes and got one for the throttle position sensor voltage out of range. I tested the sensor and sure enough it was 1.34v with closed throttle and 4.75v at wide open throttle. I searched for a while for a Motorcraft brand replacement but I couldn't for the life of me find one for my year/make so I settled for a Walker brand. When it arrived I threw it in and tested it with the multimeter and I got the same exact numbers. This has me a bit stumped. Did I actually just have two sensors with the same incorrect voltage or is there something else that might be happening here? Bad ground? I decided to take a soldering iron to the little plastic wheel on the old TPS to melt the fins back a bit to attempt to lower the voltage at closed throttle and was able to get the reading down to 0.88v at closed throttle. I'll take it for a test drive later to see if it has any effect. I also used a vacuum gauge to see what that would tell me and the needle was moving around a lot, would go down to the area that signifies late ignition timing. I guess the next step should be busting out the timing light?

 

[franklin2]

Are you sure the throttle stop is in the right place? Put the TPS back were it's supposed to be, and then get the engine running and unplug the idle air control valve. The engine idle should drop to round 500 rpm. Pretty slow. If it's still idling fast, and you still have the high TPS voltage, your throttle stop screw is too far in. Back it out till the engine really slows. You can also back it out while reading the TPS voltage. As long as you are below 1v at idle you should be good.

After doing all this it will probably run terribly. It takes a couple of drive cycles for the computer to work the new idle settings back out. Don't forget to plug the IAC back in.

 

[RustyDusty]

Are you sure the throttle stop is in the right place? Put the TPS back were it's supposed to be, and then get the engine running and unplug the idle air control valve. The engine idle should drop to round 500 rpm. Pretty slow. If it's still idling fast, and you still have the high TPS voltage, your throttle stop screw is too far in. Back it out till the engine really slows. You can also back it out while reading the TPS voltage. As long as you are below 1v at idle you should be good.

After doing all this it will probably run terribly. It takes a couple of drive cycles for the computer to work the new idle settings back out. Don't forget to plug the IAC back in.

The throttle stop screw is actually not even engaged. Its been unscrewed by the previous owner to the point where it doesn't make contact with piece its supposed to stop. So in other words the voltage is too high even with the throttle as far closed as it will go without being stopped by the throttle stop screw.

 

[Shran]

I believe that your TPS voltage should be between 0.75 and 1.0v so I'd leave it where you've got it and see how it runs. I'd be very tempted to screw the throttle stop in so it's just pushing the throttle open a tiny, tiny bit so that the end of the stop screw catches the butterfly valve before it can beat itself to death against the throttle body walls. Watch your voltage while you do that.

Might be worth checking your timing and looking over everything for vacuum leaks. My '87 had horrible erratic/surging idle when I got it and I traced most if it back to vacuum leaks.

 

[RonD]

You will need to drill out the holes on the OLD TPS to make them slotted so you can adjust the voltage by turning the TPS, you have the correct Range in the TPS but not for its current position on the throttle body

Yes, you want .69 to .99v throttle closed, and 4.5v wide open
EDIT, yes, .88 would be fine

But I doubt that's your stalling problem, I would clean the IAC Valve

TPS is not there to set idle, it has two main functions, #1 is instant throttle response, the MAP(or MAF) sensor is not fast enough to react to throttle opening, so engine would stumble unless computer got the "heads up" that more air is coming
TPS does for EFI(fuel injection) what the Accelerator Pump did on a carb, allows instant throttle response

#2 is shutting off fuel injectors, one of the biggest gas saving methods for EFI is that the flow of gasoline can be cut off when its not needed, couldn't do that with a carburetor.
When you are driving and take your foot off the gas pedal the computer will see that by TPS voltage, and it will turn OFF the fuel injectors until RPMs drop below 1,400 or so then it will turn them back on at idle levels
So when you are coasting down a hill leave vehicle in gear and fuel use is 0
With a carburetor you would want to shift to neutral when coasting because high vacuum sucked out more fuel from idler Jets, lol

But once engine is running, above 400rpms the TPS only does these two things, which are important, but wouldn't cause stalling

Idle level is set by computer using the IAC Valve, and computer has "target" RPM based on engine temp(ECT sensor)
Cold engine idles higher, 1,000+ RPM, as engine warms up the idle drops lower
With an automatic warm idle is usually 750-800rpm, and bumps up 50rpm when "in gear" or AC is turned on
That's all done by computer, IAC valve, no input from TPS

 

[RustyDusty]

Very informative post. The IAC appears relatively new, replaced by the previous owner. Inside the IAC is completely spotless surprisingly. Seems like the previous owner replaced a lot of parts trying to track down the issues I'm working on. He did a lot of the things I've read might help.

 

[RonD]

IAC Valve needs to be Motorcraft or Hitachi brand

If that's not what it is then hit wrecking yard to get a replacement
Ford uses a true solenoid IAC Valve, other brands are stepper/solenoid so will be erratic if used with Ford controls

 

[franklin2]

If you have the idle stop screw backed all the way out, and unplug the IAC and the engine still runs, you are getting air from somewhere else. The throttle butterfly when it's closed should be able to stall the engine.

 

[RustyDusty]

If you have the idle stop screw backed all the way out, and unplug the IAC and the engine still runs, you are getting air from somewhere else. The throttle butterfly when it's closed should be able to stall the engine.

As far as I can remember the engine does stall when I unplug the IAC.

 

[franklin2]

As far as I can remember the engine does stall when I unplug the IAC.

Adjust the throttle stop screw till you get a very slow idle when the IAC is unplugged. That may make the stalling go away. There is a minimum air setting for the throttle butterfly, and then the rest of the idle air is controlled by the computer and the IAC.

Keep an eye on that TPS minimum voltage. There is a transistion voltage where the computer goes from idle strategy to a regular higher rpm strategy. I believe it is around 1volt or so, so try to stay below that.

And like I mentioned, turning in the throttle stop to make it idle with the IAC unplugged, and then plugging in the IAC may give you a very high idle. Don't panic. Drive it, turn it off, then drive it, then turn it off, it should slowly figure out the new settings.

 

[Jamie Reid]

I’ve been working very hard to find the correct information in order to calibrate the tps and throttle body idle screw correctly on my 1988 2.3 and to hopefully resolve my issue. The idle screw has been tampered with in the past, so I have to figure this out.

The truck is stuck in limp mode I assume. It runs pretty bad for about a minute after the engine is started until it adjusts out and finds idle, doesn’t matter if engine is cold or hot. Runs richer than a Wall Street treadmill and will not exceed 2000 rpm on the highway. The replacement I am using is a slotted/ adjustable tps made by walker products, it’s the same style as the one I removed.

When back probing the green signal wire I am unable to bring the voltage down past 0.98 volts at closed, and I believe that is still too high rod a reading for closed voltage from what I’ve read. That being said, wide open throttle is reading close to or right at 14.0 volts, which makes no sense to me because everything I’ve read indicates WOT to be around or just under 5.0 volts. If it makes sense at all to someone on this forum, I would love to hear what you have to say, and if I am doing something wrong I would like the chance to correct it.

 

[superj]

your vacuum gage should give you some indication of things too, though.

at idle, what were you reading on it? you can use it to set your timing too, if you need to do that. it actually is good for a fair number of things. google the chart that shows all the readings the vacuum gage gives so you know what you are getting from it

 

[RonD]

I’ve been working very hard to find the correct information in order to calibrate the tps and throttle body idle screw correctly on my 1988 2.3 and to hopefully resolve my issue. The idle screw has been tampered with in the past, so I have to figure this out.

The truck is stuck in limp mode I assume. It runs pretty bad for about a minute after the engine is started until it adjusts out and finds idle, doesn’t matter if engine is cold or hot. Runs richer than a Wall Street treadmill and will not exceed 2000 rpm on the highway. The replacement I am using is a slotted/ adjustable tps made by walker products, it’s the same style as the one I removed.

When back probing the green signal wire I am unable to bring the voltage down past 0.98 volts at closed, and I believe that is still too high rod a reading for closed voltage from what I’ve read. That being said, wide open throttle is reading close to or right at 14.0 volts, which makes no sense to me because everything I’ve read indicates WOT to be around or just under 5.0 volts. If it makes sense at all to someone on this forum, I would love to hear what you have to say, and if I am doing something wrong I would like the chance to correct it.

If vehicle has AC make sure its turned OFF for all the following

1988 2.3l has a distributor, so first thing you need to do is set the base spark timing
Warm engine, SPOUT connector unplugged

Adjust the Anti-diesel screw next, its not an idle screw since fuel injected engines can't have/use an idle screw, lol
Warmed up engine
Let it idle, SPOUT plugged back in
Unplug the 2 wire connector on IAC Valve, idle should drop to about 600-650RPM on a 2.3l
If engine stalls turn screw clockwise a full turn, and restart engine
Set screw so engine is barely idling, about 650RPM
Its now set

Plug back in IAC valve and RPMs should go up to 750 to 850 depending on manual or automatic transmission
If idle didn't drop when IAC Valve was unplugged then you have a vacuum leak

Engine OFF, warm or cold doesn't matter, key on
Use a sewing needle/pin to test center wire on TPS
Throttle close should be 0.69 to 0.99volt, 0.98v is fine
Open throttle slowly and voltage should go up smoothly and be at 4.5-4.7volt at wide open(WOT)
Adjust TPS for these voltages

Yes, TPS is a 5volt sensor, all sensors are 5volt, just FYI
TPS is there to prevent engine from stumbling when accelerating and to turn OFF injectors when coasting
MAP or MAF air sensors can't respond fast enough to higher air flow, computer needs instant information so it can add more fuel as soon as gas pedal is pressed or engine would stumble
TPS does what Accelerator pump did in a Carburetor, instant fuel added

ECT(engine coolant temp) sensor is 5volt, and computer uses it on start up to set Choke level
So odd startup issues that clear up after a minute or so can be failing ECT sensor
Its reporting extreme cold or hot temp with key on, so computer is using the wrong fuel mix at startup, warm or cold

Just FYI, Coolant temp SENDER is 12volts and only used for dash board gauge
ECT sensor is only used by computer

 

[Jamie Reid]

If vehicle has AC make sure its turned OFF for all the following

1988 2.3l has a distributor, so first thing you need to do is set the base spark timing
Warm engine, SPOUT connector unplugged

Adjust the Anti-diesel screw next, its not an idle screw since fuel injected engines can't have/use an idle screw, lol
Warmed up engine
Let it idle, SPOUT plugged back in
Unplug the 2 wire connector on IAC Valve, idle should drop to about 600-650RPM on a 2.3l
If engine stalls turn screw clockwise a full turn, and restart engine
Set screw so engine is barely idling, about 650RPM
Its now set

Plug back in IAC valve and RPMs should go up to 750 to 850 depending on manual or automatic transmission
If idle didn't drop when IAC Valve was unplugged then you have a vacuum leak

Engine OFF, warm or cold doesn't matter, key on
Use a sewing needle/pin to test center wire on TPS
Throttle close should be 0.69 to 0.99volt, 0.98v is fine
Open throttle slowly and voltage should go up smoothly and be at 4.5-4.7volt at wide open(WOT)
Adjust TPS for these voltages

Yes, TPS is a 5volt sensor, all sensors are 5volt, just FYI
TPS is there to prevent engine from stumbling when accelerating and to turn OFF injectors when coasting
MAP or MAF air sensors can't respond fast enough to higher air flow, computer needs instant information so it can add more fuel as soon as gas pedal is pressed or engine would stumble
TPS does what Accelerator pump did in a Carburetor, instant fuel added

ECT(engine coolant temp) sensor is 5volt, and computer uses it on start up to set Choke level
So odd startup issues that clear up after a minute or so can be failing ECT sensor
Its reporting extreme cold or hot temp with key on, so computer is using the wrong fuel mix at startup, warm or cold

Just FYI, Coolant temp SENDER is 12volts and only used for dash board gauge
ECT sensor is only used by computer

Perfect,
I appreciate your time, and I will do these steps this evening when I am able.
Would any of these steps or anything related to them be the reason I am getting 14 volts at WOT at the signal wire? I’ve replaced the ETC sensor mounted in the intake, I’ll have to test for voltage.

 

[franklin2]

When reading your voltage, on the TPS, put your black meter lead on the black/white instead of a convenient ground. The black/white is the true ground for the 5v supply. While it should be close to the same, if it isn't, that may be a clue.