According to my BlueDriver scan tool, the throttle position of my 02 Mustang GT is 20% at idle while it is only 3% on my 14 Xterra. Is that normal for the Mustang or do I need to take some kind of action on the throttle body?
Seems high. Have you got a fresh air filter in there?
If yes, then I would make sure the throttle body is clean.
The filter is clean but I haven't inspected the throttle plate. It has never been cleaned. I suppose that if the plate is clean then the sensor must be bad?
not necessarily. May just need computer calibration.
I just cleaned the throttle plate and it's still 20% at idle. I tried the power drain to reset all the electronics but it didn't clear the problem. There are no codes tripped. Time for a new sensor? They don't look expensive but I'd rather not replace it if I don't need to. But it is a 20 year old sensor.
power drain doesn't reset things like that. run a throttle calibration/relearn with a good diagnostic tool.
I don't have anything that'll do that. Besides, this is a cable operated throttle, not an electronic throttle.
look at the throttle plate when the engine is idling. Is it completely shut, or is it 20% open?
Couldn't tell. Disconnecting the air intake hose killed the engine. With the air intake hose disconnected, the throttle plate appears to be completely closed though. Pushing on the plate wouldn't close it any further. As near as I can tell the throttle plate should be completely closed during idle based on the position of the linkage - there was no change in position until revving the engine. I disconnected the linkage spring but it didn't make any difference. I was going to try to reseat the sensor but I'll have to wait awhile for the penetrating oil to do its thing since the mounting screws are very tight. I read that there can be a slight adjustment to the sensor to get a specific voltage out of it. Don't know what else I can do right now. Photo: https://www.amazon.com/photos/shared/KKoFYxETQiSJpxxhA3LldA.7B5tOR2QPbqhRLcXLHLRFf
Does the bluedriver TPS reading change as you press the accelerator? What does it say when it's fully depressed (you should be able to do this with the engine stopped, key in run position).
I still think there's a chance the sensor needs to be calibrated in the computer with a proper tool. If not, then yeah I'd say the sensor is malfunctioning.
Goes from 20% to 93%.
The TPS is a potentiometer. It's a manually adjustable variable resistor.
It doesn't tell the PCM the Throttle position angle. It sends a voltage signal to the PCM and the PCM is the guy who interprets that voltage signal into Throttle Angle.
The TPS has 3 wires. One receives a 5 volt reference from the PCM. One receives a Ground provided by the PCM. The third wire is the Signal wire which outputs a voltage signal back to the PCM.
It looks like this:
The PCM learns what that voltage signal represents and displays it as Throttle Angle.
So no matter what the computer learned (or hasn't learned) about how that voltage signal relates to throttle angle, all of the voltages can be measured at the TPS to see if it's working right.
Measuring the 5 volt reference is easy enough. It's 5 volts.
Checking the Ground is easy enough too.
On the Signal wire, throttle closed on your Mustang should be between 0.6 and 0.9 volts.
Throttle wide open should be around 4.5 volts.
Your scanner may be able to display the TPS Signal voltage so you can watch that (Key ON, Live Data) as you press down on the accelerator pedal.
If your scanner can't read the TPS voltage, you can do it with a multimeter.
Here's how:
https://easyautodiagnostics.com/ford/4.6L-5.4L/tps-diagnostic-tests-1
If the voltages look right then there isn't a problem with your TPS sensor and you'll want to perform the relearn again and you have to be patient.
The best time to do this is before the 1st start of the day.
When you disconnect the battery Ground cable and jump it to the battery Positive cable give it at least 3 minutes to drain the capacitors in the PCM to kill the KAM (Keep Alive Memory).
Then make sure nothing is on (A/C, Blower motor, Lights, etc) and start the Mustang from a cold start and let it idle/warm up for at least 15 minutes.
The PCM has to learn idle at cold through warm temperatures first because everything else it learns (shift points, etc) is based on those voltage values.
Then take it for a leisurely drive through town and then on the highway. Drive it like you always drive it.
One more thing. I've seen throttle position angles up to 25% on Fords at idle. As long as they're running good, the fuel trims look good, and there aren't any TPS circuit or voltage codes, I've never worried about it.
I don't like to micromanage. My philosophy is, if it ain't broke, don't fix it.
Good point Jack. I've heard that some modern engines with independent intake valve timing can control (to a degree) the volume of intake air by phasing valve timing. This allows a more open throttle, which reduces pumping losses, increasing engine efficiency.
However, if the throttle is actually shut, then the TPS angle should still indicate close to 0%.
He mentioned it's a mechanical throttle. Wouldn't that mean that it SHOULD be shut at idle, and airflow is controlled by the IAC valve?
That has been my understanding - that the IAC allows airflow when the throttle valve is fully closed. The 02 Mustang does have an IAC valve that can be removed for cleaning and I cleaned it a few weeks ago. Anyway, I'll check these throttle sensor voltages sometime today. By the way, what is the tolerance for the 5V? 0.1? 0.01? I have a Fluke 77 multimeter so checking at the sensor will be no problem. I don't see anything on the BlueDriver that would indicate voltage.
well 1% of 5V is 0.05 V
That seems reasonable to me.
We know his throttle plate is closed at idle otherwise he'd be asking, "Why is my Mustang idling at 2,000+ rpms?"
Think about it. If the throttle angle was actually at 20% at idle, what could the computer do about it?
The MAF would read that airflow and the computer would have to provide the correct fuel for 14.7:1.
What else could the computer do? Shorten the injector pulses to try to cut fuel? It just doesn't work that way.
Even if it did, the upstream O2 sensors would get stuck lean and with that kind of a computer/O2 sensor conundrum his Mustang would be throwing codes galore.
Like I said, here I think it would be a good idea to either manually check the 5 volt reference and Ground and Signal voltage with a multimeter or at least (if his scanner is capable) observing the TPS signal voltages as he
goes from not pushing on the accelerator pedal through wide open throttle.
It seems to me that the computer has determined that idle is at throttle plate position 20%.
So is it a voltage issue? Maybe the 5 volt reference is shorting to a 12 volt wire, or there's a crappy ground, or is it just that the computer needs a good relearn lesson.
Yes, the throttle is actually closed . Eel has already confirmed that. The issue seems to be the TPS sensor reading. It should be 0% at idle, right?
You're absolutely correct. Ideally, the throttle angle should be close to zero or maybe + a few degrees at idle
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Since he's confirmed that his throttle plate is closed at idle it just comes down to who's lying. The TPS sensor or the computer
It has 4.977VDC applied with the signal output of 0.988VDC at idle and 4.621VDC at WOT. The ground wire (common) is not the same as chassis ground. All voltages were measured with reference to common (not chassis/frame ground). I guess the BlueDriver sees the 0.988VDC as 20% instead of zero? I would assume that the BlueDriver would've accounted for this? I'll fire off an e-mail to BlueDriver and see what they say.
0.988 is 16% of 4.977 so maybe nobody is lying.
Is it possible there are two different throttle values? One raw, and one compensated (since the engine runs OK). Maybe the 20% you saw was the the raw uncorrected value. Maybe there's another throttle parameter which does actually show 0%?
The Ground is provided by the PCM
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The 4.977VDC is the 5 volt reference and it doesn't get any closer than that
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The Signal 0.988VDC at idle and 4.621VDC at WOT looks close to perfect also
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Be careful. Don't confuse these "raw" sensor voltages to what you're seeing as the throttle position % on your scanner
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You just confirmed that your TPS sensor is functioning correctly
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I'd perform the relearn procedure again just the way I posted it in a previous reply
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I am with MMJoe on this one. Either the throttle plate is crudded up or the cable is misadjusted or binding in the 20% position.
I agree with @mmj and @doc. The 20% throttle position sounds to high. That engine should idle smoothly at 1000 RPM on a cold start and drop to a smooth 750-800 RPM when sufficiently warm. If it does your TSP is working correctly. The symptoms of a malfunctioning TPS are rough idle, slow or fast idle, stalling and hesitation. If the engine is running OK I would suspect bad info. coming from the blue driver. I am quite sure if the throttle plate is really open 20% the idle speed would be over 2000 RPM. If the TPS is telling the computer the plate is open 20% when it isn't the engine would not run correctly. I hope this helps.
It's at 550 RPM at idle with the AT in Drive. It's about 750 RPM in Park. Engine is at operating temperature (190 degrees Fahrenheit). I don't think it's a problem with the BlueDriver since it shows 3% throttle at idle on my Xterra.
Fuel economy for the Mustang is 14.5 MPG for city driving. EPA average is 17 MPG.
The car sounds like it's running right. I have one of those cars with a manual trans. so I'm not familiar with exact RPS in Drive but 550 sounds perfect. The reason I suspect bad info from the BlueDriver is because the Mustang has a relatively primitive computer and may not provide all the data the BlueDriver needs. I don't know why it's telling you 20% but I think that's wrong for the reasons I gave above. It sounds like it works well on the more sophisticated Xterra computer. I would bet 3% is absolutely correct there. Also, it is very difficult to achieve actual EPA averages in real world driving so I wouldn't gauge much by a 2.5 MPG difference. Those cars will swallow up some gas if you don't keep your foot light. Good luck with the Mustang.
I reset the electronics by jumpering the positive and negative cables together for 1 hour. I did the idle relearn after that. But it didn't change anything as far as throttle position goes. It's still showing 20% on the BlueDriver at idle after driving for a couple of days. I'll report it to BlueDriver but I doubt they'll be able to do anything in their software to compensate for this. The car drives OK otherwise.
I was thinking 2% is correct and the BlueDriver is multiplying by 10 for some reason. As I recall there are stops built in to the throttle body that prevent the plate from fully closing. That's about 2% I think.
OK, so a couple of weeks ago I connected my THINKCAR scan tool to my 2001 GT and found the throttle position showing 20% at idle just like yours. I did some investigating and here's what I've come up with:
The TPS output signal to the computer is a voltage that ranges from approx. 1 volt at idle (throttle plate as closed as it can be) to approx. 5 volts at WOT. (equal to the reference voltage) 1 is 20% of 5, so for whatever reason the throttle position is expressed by the scan tool as a percentage of the signal voltage versus the 5 volt reference, rather than the actual throttle plate position.
Based on your measurements back in November everything seems to work out. 0.988v/4.977v=0.198v=19.8% I'm thinking the scan tools round the percentage to the nearest whole number, so there you are at 20% throttle position idling on your BlueDriver.
I have not done any testing to verify, but it makes perfect sense to me now. My TPS was replaced with a new one last summer for reasons I won't elaborate on, but your 20 year old sensor seems to be doing the exact same thing as my new sensor. I think it's good. The below video describes testing an older Ford TPS, the truck looks quite similar to my old 2003 F-150. It's the same as the test @jack62 provided back in November but it doesn't explain the percentages as seen on the scan tools.
Thanks for the info. I would have thought that the ECM would calculate and report to a diagnostic tool as 0%. I'll have to keep this in mind. I did replace the TPS and got the same result as the old TPS. I have a lot of mode 6 info, also, that just says "Manufacturer defined test" - most come out green but some are red - I have no idea what they are reporting on. Anyway, I have to say that I'm impressed as to how well this car has held up over 20 years of service despite not maintaining it as well as I should have. On the other hand, I only have 72,500 miles on it. I wonder if it'll make it another 72,000 miles......
With no problem at all if you take good care of it. I have more than double your mileage and the car is still in great condition. There's no telling how long it will last. My kids might inherit the thing. 😆