TPS PFC VTA1 Erratic
09-30-18, 07:52 AM
#1
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TPS PFC VTA1 Erratic
I’ve recently replaced all the vacuum lines and emission harness. Initially the car was running great but I’ve noticed that the idle is fluctuating and light throttle movements are causing the car the buck. When bucking occurs the voltage on VTA 1 is also fluctuating.
I suspect the tps sensor has failed. VTA 1 is doesn’t change with throttle movement. It’s stuck between 4.7 and 4.88 volts. When the idle becomes erratic it will fluctuate between 2 and 4.88 volts. VTA 2 range is normal from .8 v to 4.8 v. I have tried adjusting the sensor but can’t get tps 1 to change. The throttle cable is loose and the car is warmed up when I adjusted the tps.
Is this indicative of a failed tps sensor or should I be concerned with the new wiring harness or something else?
I suspect the tps sensor has failed. VTA 1 is doesn’t change with throttle movement. It’s stuck between 4.7 and 4.88 volts. When the idle becomes erratic it will fluctuate between 2 and 4.88 volts. VTA 2 range is normal from .8 v to 4.8 v. I have tried adjusting the sensor but can’t get tps 1 to change. The throttle cable is loose and the car is warmed up when I adjusted the tps.
Is this indicative of a failed tps sensor or should I be concerned with the new wiring harness or something else?
09-30-18, 01:10 PM
#2
With a digital multimeter u can test the tps.
Unplug the tps and measure the resistance of the narrow range as you slowly move the throttle linkage by hand. It should smoothly transition if there is any point it causes an open (maxed out resistance) or jumps erratically. Then the sensor is at fault.
if it checks out fine there, then look into the wiring
Unplug the tps and measure the resistance of the narrow range as you slowly move the throttle linkage by hand. It should smoothly transition if there is any point it causes an open (maxed out resistance) or jumps erratically. Then the sensor is at fault.
if it checks out fine there, then look into the wiring
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Alchemyst6 (09-30-18)
09-30-18, 05:23 PM
#3
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Okay, I measured the narrow range(red/green) and full range (black/green) to the ground (brown/black wire). Here are my results...
Narrow: Closed 62 ohms, wide open 1.513 kohms. It is linear from closed to about 1/3 open (1.498 kohms) then from 1/3rd to full open it fluctuates slightly and inconsistently between 1.5 and 1.62 kohms
Full: closed 129 ohms, wide open 231 ohms. It is also linear to 1/3rd open peaking at 1.961 kohms. Them from 1/3rd to full open it drops fairly linearly back to 231 ohms.
Additionally, on the connector side there is continuity on the ground wire and 5v on the power wire.
I haven’t been able to find any information regarding ohms scale on the tps. It seems this could be the culprit but that may be the way the sensor operates normally too.
Narrow: Closed 62 ohms, wide open 1.513 kohms. It is linear from closed to about 1/3 open (1.498 kohms) then from 1/3rd to full open it fluctuates slightly and inconsistently between 1.5 and 1.62 kohms
Full: closed 129 ohms, wide open 231 ohms. It is also linear to 1/3rd open peaking at 1.961 kohms. Them from 1/3rd to full open it drops fairly linearly back to 231 ohms.
Additionally, on the connector side there is continuity on the ground wire and 5v on the power wire.
I haven’t been able to find any information regarding ohms scale on the tps. It seems this could be the culprit but that may be the way the sensor operates normally too.
Last edited by Alchemyst6; 09-30-18 at 05:32 PM. Reason: Add i
09-30-18, 05:31 PM
#4
You don't need a multimeter with a power fc as it displays the voltages for you. The absolute way you can verify your tps is bad is to remove it from the throttle body, plug it in to the harness and watch the vta readings as you manually rotate the spring on the back. If you get the same funky fluctuations then the tps is bad. If you don't, then it may be possible that the tabs on the back of the tps are not properly set In the space on the throttle body..... which I hope is the case because another tps is expensive.
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Alchemyst6 (09-30-18)
09-30-18, 05:42 PM
#5
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Cr-Rex, thank you. I tried this and voltage seems to be reading normally. I’ll put the sensor back in the car and give it another try. Funny thing is that I removed the throttle body from the uim when I did the harness and vacuum lines but I never removed the sensor. Perhaps removing the throttle body caused the ears to miss align.
09-30-18, 05:48 PM
#6
If you get normal readings turning it manually but erratic with it on the throttle body then your problem is with the throttle body or your tps is having intermittent problems, which is the worst thing ever. It makes troublseshooting a pain since the problem only happens when it wants. I would keep twisting the tps through it's range like 20-30 times just to be sure it's not intermittent and the problem is not with the tps. While watching the vta values of course...
the tabs on the tps won't come out of its home without being removed, so just removing the tb won't/shouldn't cause tps issues unless you hit it on something pretty hard. But once engaged, it's impossible for the tabs to be not engaged unless they break off entirely
the tabs on the tps won't come out of its home without being removed, so just removing the tb won't/shouldn't cause tps issues unless you hit it on something pretty hard. But once engaged, it's impossible for the tabs to be not engaged unless they break off entirely
09-30-18, 06:50 PM
#7
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Everything is running perfectly now. Thanks for the help guys! I’m not sure what caused it to get out of alignment though. Never dropped the tb while it was off.
Last edited by Alchemyst6; 09-30-18 at 06:54 PM.
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10-01-18, 09:44 AM
#8
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Well that was short lived. It actually appears to be the harness connection at the PFC. The VTA 1 wire has to have an intermittent connection. I guess in the process of troubleshooting I inadvertently corrected the problem only to have it come back when I moved the computer.
10-01-18, 10:46 AM
#9
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Been thinking about this kind of thing recently. I read some info from GM/Delco that spoke about how problems could develop at the ECM harness connection if the ECM is unplugged and reconnected too many times. Apparently this came from work on prototype vehicles with development ECM's were changed out repeatedly and random electrical problems developed. They investigated with the harness guys and it was learned that about 12 plug/unplug cycles were the maximum recommended for a harness plug before the possibility of poor connection due to wear or loss of spring tension could occur. Something to think about as we swap out ECM's over and over for various reasons.
Last edited by jza80; 10-01-18 at 02:42 PM. Reason: spell check
10-01-18, 10:54 AM
#10
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Good to know jza80. Fortunately I purchased a new harness recently and have only plugged it in a few times. I think during the depinning procedure that pin may have worked itself back in the connector, causing the intermittent connection. I’m going to check it today and reset it if needed. I only found out about this when I went to move the pfc back to the foot panel while the car was running. The idle jumping again like before. It’s a good thing I found out this way because I’m certain this intermittent problem would have presented itself again after everything was back together.
Edit... The issue was due to an intermittent connection of the narrow range wire at the pfc harness. Fixed now.
Edit... The issue was due to an intermittent connection of the narrow range wire at the pfc harness. Fixed now.
Last edited by Alchemyst6; 10-02-18 at 09:26 AM. Reason: Add info
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