After trying many different things such as checking vac lines, isc, etc. to see if any would affect my rough idle problems, i tried unplugging the tps because i hear that it can sometimes cause rough idle. My observations prior to unplugging to tps were: vac at 16-17, fairly smooth idle at around 650 but sometimes lowers to 450-550 (and vac lower at about anywhere from 10-16, with any combination of being steady or surging with rpms) where the idle surges for a long bit until it manages to bring itself back up to about 650. Observations after unplugging tps: vac of 18-19, a bit higher idle at around 700-800 but never lowered below 650 (seemed to be running better... weird?), still a slight surging could be heard but im not too worried about it (very faint). So what is up with that? is that a common symptom of a dead tps? With the tps plugged in, if idling and i do a quick rev up to anywhere from 2500-3500 rpm, the rpms will then drop to the stage of 450-550 rpm surging, but if in this state and i slowly bring the rpm up to 1000, the surging stops and the idle returns back to around 650. This sequence of events does not carry over to when the tps is unplugged because, like i said, the rpms do not do the low idle surge. After driving with the tps plugged in i noticed that when i stopped to idle the rpm was higher around the 900-1000 range. I tried testing the tps with an ohm meter like in the tsrm but i was getting no results so i may throw that out because of the cheap meter. Any ideas guys?
common dead tps symptoms? (very detailed problem writeup)
- Thread starter 88SupraTurbo
- Start date
As a matter of fact, I got a code 41 (TPS) today. I have had similar problems and the wierdest thing is that they'll come and go.
Do you have bucking, stumbling and hesitating under throttle as well?
I came to the realization of having a bad TPS today while scanning through my TSRM. I saw the illlustration of the tach surging between 1200-1600 RPM. After reading what it said about it, I've had the exact problem with my engine for a while (like I said, off and on) and I finally know what's wrong.
Yup, I'd put my money on the fact that you have a bad TPS as well.
-Craig
Do you have bucking, stumbling and hesitating under throttle as well?
I came to the realization of having a bad TPS today while scanning through my TSRM. I saw the illlustration of the tach surging between 1200-1600 RPM. After reading what it said about it, I've had the exact problem with my engine for a while (like I said, off and on) and I finally know what's wrong.
Yup, I'd put my money on the fact that you have a bad TPS as well.
-Craig
no i have no problems under throttle with it either plugged in or not. It runs great all the time excpept for idling... and i dont have the surging from 1200-1600, only 450-550. The surging from 1200 to 1600 does sound like how it was when my isc was unplugged.
hey guys I was testing my TPS and all the resistances were as the TSRM said it should be, except for when the throttle is open to .5mm At that point the resistance jumps around between 50 ohms and 1800 ohms. Could this cause a very bad misfire at light throttle?
What pins? There are two separate parts of the TPS and they do different things.
I seriously doubt your problem is TPS related but it's easy enough to check. Your problem sounds more like a ICS problem or vacuum leak. A TPS can develop a flat spot at it's usual driving position so you might check for that. You also might want to search the forum as much has been written regarding TPS checking.
The surging SP 7M mentioned is caused by the TCCS fuel cut. Not the fuel cut most talk about here but the one the ECU uses when it sees a conflict between airflow and throttle position.
I seriously doubt your problem is TPS related but it's easy enough to check. Your problem sounds more like a ICS problem or vacuum leak. A TPS can develop a flat spot at it's usual driving position so you might check for that. You also might want to search the forum as much has been written regarding TPS checking.
The surging SP 7M mentioned is caused by the TCCS fuel cut. Not the fuel cut most talk about here but the one the ECU uses when it sees a conflict between airflow and throttle position.
yes, as per TSRM i checked both sets of pins and everything checked out, the only problem was the resistance at .5mm open throttle was very bouncy and jumped from 50 ohms up to 1.8k ohms and back down very sporadically.
I'm just wondering that if that one setting is that out of whack will it cause a bad stumble and hesitation at light throttle situations?
Edit: The TSRM calls for 2.3k ohms or less at .5mm open throttle, so the resistance is in the correct range it just jumps around.
I'm just wondering that if that one setting is that out of whack will it cause a bad stumble and hesitation at light throttle situations?
Edit: The TSRM calls for 2.3k ohms or less at .5mm open throttle, so the resistance is in the correct range it just jumps around.
The bucking,stumbling (kind of like a miss fire?) I had that along with idle surge and stalling problems when I purchased my mk3. I removed the ISC valve and cleaned thoroughly with carb cleaner, replaced the gasket and washer (cost around $5) and no more problems (knocks wood). Also remove the 3k pipe and clean the carbon deposits off the TB. Good luck with it.
Again, what pins are doing this? The TPS is both a switch and a potentiometer.
If it's the IDL contacts that could explain your problem as they're used to activate the ISC system. Are you getting a code 51? Short the diag connector and turn the key on. Press the gas pedal slightly and you should see a code 51. Release the pedal and the code should go back to normal. This is a quick and dirty way to check the IDL contacts without using a meter.
If it's the VTA pins that are giving you bum readings it'll be a different story. Too bad you don't have a scope at it'd show you visually exactly how healthy the TPS is
The TPS doesn't carry as much weight in the scheme of things compared to other sensors. The ECU uses it to look at how fast the throttle is being opened more than it's position. It's the rate that matters. Think of it like an accelerator pump on a carb. The AFM is primary for sensing engine load. A bad TPS (a flat spot on it for example) will cause stumble during acelleration but shouldn't matter at light throttle crusing. On the other hand if the IDL contacts don't close when the throttle is closed it'll goof up your idle, since they tell the ECU to turn on the ISC system.
After all, you don't want the ISC system to be operating when you're not at idle. The IDL contacts are what turn it on and off. They're the reason for all that monkey motion the manual tells you to go through when adjusting the TPS
If it's the IDL contacts that could explain your problem as they're used to activate the ISC system. Are you getting a code 51? Short the diag connector and turn the key on. Press the gas pedal slightly and you should see a code 51. Release the pedal and the code should go back to normal. This is a quick and dirty way to check the IDL contacts without using a meter.
If it's the VTA pins that are giving you bum readings it'll be a different story. Too bad you don't have a scope at it'd show you visually exactly how healthy the TPS is
The TPS doesn't carry as much weight in the scheme of things compared to other sensors. The ECU uses it to look at how fast the throttle is being opened more than it's position. It's the rate that matters. Think of it like an accelerator pump on a carb. The AFM is primary for sensing engine load. A bad TPS (a flat spot on it for example) will cause stumble during acelleration but shouldn't matter at light throttle crusing. On the other hand if the IDL contacts don't close when the throttle is closed it'll goof up your idle, since they tell the ECU to turn on the ISC system.
After all, you don't want the ISC system to be operating when you're not at idle. The IDL contacts are what turn it on and off. They're the reason for all that monkey motion the manual tells you to go through when adjusting the TPS
Ok here's the deal, the TSRM says to test the IDL and E2 contacts for slightly open throttle and then the VTA and E2 for fully open and fully closed throttle.
The IDL contact is the one that is giving me problems. But my car idles flawlessly. My problem is a misfire that comes on at slight acceleration/light throttle.
Edit: I have tried multiple things i.e. replaced all vacuum lines, new plugs and wires, checked coil pack ground, tested coils, cleaned ISC valve(which was already spotless when removed) also cleaned check valve and gasket in intake manifold behind the ISC.
My car runs perfectly without a misfire until it is fully warmed up, if that helps.
The IDL contact is the one that is giving me problems. But my car idles flawlessly. My problem is a misfire that comes on at slight acceleration/light throttle.
Edit: I have tried multiple things i.e. replaced all vacuum lines, new plugs and wires, checked coil pack ground, tested coils, cleaned ISC valve(which was already spotless when removed) also cleaned check valve and gasket in intake manifold behind the ISC.
My car runs perfectly without a misfire until it is fully warmed up, if that helps.
IDL and E2 should be closed when the throttle is closed. If they're not you'll get code 51. As long as you don't get that code the ECU is satisfied. The car may idle great with the IDL contacts open but the ISC will be disabled ie, it won't respond to changes in idle. A quick check is to turn your AC or headlights on and see if it increases a few hundred rpm. It sounds like your IDL contacts are OK. You could always clean them up using a small constant current power supply but I'm guessing you don't own one of those.
Besides, a bad IDL contact will not cause misfire at part throttle. However, if the opposite happens (if IDL stays closed when off idle with a bad TPS) the ECU will go into rpm cut mode. Since you aren't having this problem that's just FYI.
VTA and E2 is for throttle position. The resistance should be as speced and not have any drop off or erratic changes as the throttle is smoothly operated from closed to full open and back again.
Sounds like your TPS is OK so I'd look elsewhere. Misfire on light pedal can be caused by any number of things. Could be mixture related (lean or rich misfire), valve deposits, ect. You have to find out if it's fuel or spark related. If it isn't there at idle it's *probably* not ignition related. That said, it could still be something in the primary or secondary igniton circuit breaking down. How's the CPS and wiring look? Only when warmed up? Hows the O2 signal look?
You're suffering the worst kind of symptom: a mild drivibility one. Those can be tough to solve without the right diagnostic gear. I'm afraid I can't offer much more than this without actually being there.
Besides, a bad IDL contact will not cause misfire at part throttle. However, if the opposite happens (if IDL stays closed when off idle with a bad TPS) the ECU will go into rpm cut mode. Since you aren't having this problem that's just FYI.
VTA and E2 is for throttle position. The resistance should be as speced and not have any drop off or erratic changes as the throttle is smoothly operated from closed to full open and back again.
Sounds like your TPS is OK so I'd look elsewhere. Misfire on light pedal can be caused by any number of things. Could be mixture related (lean or rich misfire), valve deposits, ect. You have to find out if it's fuel or spark related. If it isn't there at idle it's *probably* not ignition related. That said, it could still be something in the primary or secondary igniton circuit breaking down. How's the CPS and wiring look? Only when warmed up? Hows the O2 signal look?
You're suffering the worst kind of symptom: a mild drivibility one. Those can be tough to solve without the right diagnostic gear. I'm afraid I can't offer much more than this without actually being there.
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