TPS or Idle problem
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  1. #1
    Newbie mechwarr has not yet proved knowledgeable
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    Default TPS or Idle problem

    Guys, I need an advise - I'm outta ideas
    I've Elantra 2002 GT.
    My idle rpm was jumping from 1500 to 3000, and later on it stays at 4000 a moment I turn the car on (doesn't matter hot or cold). I got a Memoscan tool and it showed the p0121 problem. Right away I bought a new TP sensor and installed it. But nothing changed. I don't remember where, but on this forum, I found a doc file named "TPS.doc" which says how to test TPS and harness. After testing I found that even my old TPS was good. All the measurements were in the norm, but I noticed that in this doc file the pin names are confused - one should interchange the 1 and 3 pinnames. Anyway, I tested both old and new TPS - readings were almost identical. My next step was to test the harness. All was according to this doc file [i.e. while jack is disconnected and ignition is ON, potential on pin 3 was 4.8 volts, ground (pin 2) was continuous], but I couldn't properly test the 1 pin, which is the signal from TPS to ECU. In the doc it says to ground the 32 pin of the ECU and at the same time check the 1 pin to ground. I couldn't disconnect the ECU jack, so I measured the resistance of between 1 pin and ground in was 65 KOhms. And I don't know is that good or not. So, everything seems to be OK, but the car is still at 4000 rpm, and scan tool still shows the p0121 error.
    Does anyone has any ideas? I would appreciate also if someone could spare a wiring diagram of the ECU and sensors part, so I could check the connections and/or shortcuts or discontinuities.

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  3. #2
    Ninja Super Mod KeWLKaT knows a lot about Elantras KeWLKaT's Avatar
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    Default Re: TPS or Idle problem

    Did you reset the ECU after installing it?

    '02 Elantra GT
    '04 Suzuki Katana 600

  4. #3
    Newbie mechwarr has not yet proved knowledgeable
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    Default Re: TPS or Idle problem

    Yes. Took off the negative terminal, then turn on the ignition.
    For first two minutes car idle was 2000 rpm, but after it warmed up it went back to 4000 and scantool showed the same error - p0121

  5. #4
    Kinky Kelly 2003GT has not yet proved knowledgeable 2003GT's Avatar
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    Default Re: TPS or Idle problem

    What about the idle air motor. Some cars have a bypass that lets only a certain amount of air through at idle. Maybe that motor is gone. Either that or you have a bum head gasket and air is getting into the system. BOB

  6. #5

    Default Re: TPS or Idle problem

    For the engine to stick at 4000, something has to be holding the throttle open pretty wide. Since there is no drive by wire throttle that the computer controls, I would assume you have a mechanical issue with the accelerator cable. Maybe the gas pedal is stuck on the carpet or something? Or maybe it's adjusted too tight at the bracket?
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  7. #6
    Super Moderator Cypher knows a lot about Elantras Cypher's Avatar
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    Default Re: TPS or Idle problem

    I'm going to guess a vacuum leak of sorts. Take a can of carb cleaner and spray over the intake manifold and subsquent vac lines. See if the rpms drop while you're doing that.
    2002 Hyundai Elantra: Sold
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  8. #7
    xd tunner mayollo072R has picked up a wrench mayollo072R's Avatar
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    Default Re: TPS or Idle problem

    Quote Originally Posted by Cypher View Post
    I'm going to guess a vacuum leak of sorts. Take a can of carb cleaner and spray over the intake manifold and subsquent vac lines. See if the rpms drop while you're doing that.

    Agree. Vacum leak. Check your ISA motor and the accelerator cable in the TB pulley. ISA motors tend to break and leak.

  9. #8

    Default Re: TPS or Idle problem

    I thought of a vacuum leak due to his flucuating from 1500-3000. But typically, vacuum leaks cause the RPM's to drop, and sometimes stall. So when he said it was stuck at 4000, I thought it couldn't be a vacuum problem. I've never really seen a vacuum leak cause a car to stick at 4000 rpm. That's really high! I'd be surprised if it was a vacuum leak.

    Try cleaning out the throttle body/plate to make sure it isn't gumming up.
    Last edited by DJ Hellfire; 05-18-2008 at 02:05 PM.
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  10. #9
    xd tunner mayollo072R has picked up a wrench mayollo072R's Avatar
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    Default Re: TPS or Idle problem

    Quote Originally Posted by DJ Hellfire View Post
    I thought of a vacuum leak due to his flucuating from 1500-3000. But typically, vacuum leaks cause the RPM's to drop, and sometimes stall. So when he said it was stuck at 4000, I thought it couldn't be a vacuum problem. I've never really seen a vacuum leak cause a car to stick at 4000 rpm. That's really high! I'd be surprised if it was a vacuum leak.

    Try cleaning out the throttle body/plate to make sure it isn't gumming up.

    When I first installed the airram i left the 1/2" vacuum line wihout a cover and that caused my rpms to a steady 4k rpm. Also whem my ISA motor broke because of a missintallation it caused a steady 3k rpm. He may also have a bad or stuck TB or even a bent TB pulley.

  11. #10

    Default Re: TPS or Idle problem

    Quote Originally Posted by mayollo072R View Post
    When I first installed the airram i left the 1/2" vacuum line wihout a cover and that caused my rpms to a steady 4k rpm. Also whem my ISA motor broke because of a missintallation it caused a steady 3k rpm. He may also have a bad or stuck TB or even a bent TB pulley.
    But a vacuum leak that large would be easy to hear, right?
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  12. #11
    xd tunner mayollo072R has picked up a wrench mayollo072R's Avatar
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    Default Re: TPS or Idle problem

    Only the one from the 1/2" vac. The other one might be tricky to hear. If is not a vacuum leak i'll think a bad or stock tb. Those are the only things that have caused me that type of problem. It could be some other thing but thats my best guess with the described symptoms.

  13. #12
    Newbie mechwarr has not yet proved knowledgeable
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    Default

    Quote Originally Posted by DJ Hellfire View Post
    For the engine to stick at 4000, something has to be holding the throttle open pretty wide. Since there is no drive by wire throttle that the computer controls, I would assume you have a mechanical issue with the accelerator cable. Maybe the gas pedal is stuck on the carpet or something? Or maybe it's adjusted too tight at the bracket?
    No, the cables are "loose" - the throttle pulley is closed, i checked it during the engine revving.

    Quote Originally Posted by Cypher View Post
    I'm going to guess a vacuum leak of sorts. Take a can of carb cleaner and spray over the intake manifold and subsquent vac lines. See if the rpms drop while you're doing that.
    I'll try this.

    Quote Originally Posted by mayollo072R View Post
    When I first installed the airram i left the 1/2" vacuum line wihout a cover and that caused my rpms to a steady 4k rpm. Also whem my ISA motor broke because of a missintallation it caused a steady 3k rpm. He may also have a bad or stuck TB or even a bent TB pulley.
    So you suggest to find and install another TB?
    Last edited by KeWLKaT; 05-19-2008 at 06:26 PM.

  14. #13
    xd tunner mayollo072R has picked up a wrench mayollo072R's Avatar
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    Default Re: TPS or Idle problem

    No, just check it. If it's ok check for vacuum leaks.

  15. #14
    Newbie mechwarr has not yet proved knowledgeable
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    Default Re: TPS or Idle problem

    Quote Originally Posted by mayollo072R View Post
    No, just check it. If it's ok check for vacuum leaks.
    I did what you guys advised me. Sprayed all the intake manifold and vac lines with carb cleaner. No changes - as it was on 4K rpm it stayed. Also I tried to clean the TB with the TB cleaner. Wile engine was working sprayed it into TB throat. Wile spraying the rpm dropped, then as cleaner evaporated it returned to 4K rpm.
    I tried to disconnect TPS and IAC (or ISP - I guess it's the same thing with different names) one by one. While TPS disconnected there were no changes in rpm at all. But when the IAC was disconnected the engine dropped to 1500-2000 and was working wery unstable and was almost nonresponsive to the gas pedal.
    So I thought - may be the problem in in the IAC?

  16. #15
    Newbie mechwarr has not yet proved knowledgeable
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    Default Re: TPS or Idle problem

    I read somewhere here that it might be helpful to take the IAC off and clean it with the carb cleaner. I did it. A lot of oily dirt came out. But when I took IAC off I noticed that inside the first nozzle (the upper one, which is not circular but a different shape) the metal cover (flap), which I suppose is driven by the actuator, is 1\8 inch slit open. I tried to displace it with a screwdriver in both directions - from fully close to fully open, (it went with no resistance) but when I took a screwdriver off this flap jumped back - to 1\8 inch open slit. Is this a good state for the IAC? may be I have to change it?

  17. #16
    Newbie mechwarr has not yet proved knowledgeable
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    Default Re: TPS or Idle problem

    Finally brought the car to the dealer. The problem indeed was in the vacuum - intake gasket was dead, not in the sensors. As many of you suggested. They changed the gasket, the RPM stabilized.
    Thanks to everyone who helped!

  18. #17
    Ninja Super Mod KeWLKaT knows a lot about Elantras KeWLKaT's Avatar
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    Default Re: TPS or Idle problem

    Glad we could help! Good luck

    '02 Elantra GT
    '04 Suzuki Katana 600

  19. #18

    Default Re: TPS or Idle problem

    I am having the EXACT same issue as you, and have tried everything you have. Even replaced the IAC with no change at all.

    How much $$$ did it cost you to have the shop do all the work?

  20. #19
    Newbie alexcjames88 has not yet proved knowledgeable
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    Default Re: TPS or Idle problem

    I've had this problem a couple of times, the first time I had the shop replace the IM Gasket, cost around $215 (with a generous mechanic). The second time, however I picked up the gasket for $15 at car quest and installed it myself. I'm no speed demon with repairs, but I got it done in a couple of hours. Hope that helps!

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