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1G High and choppy idle

Posted by mitsuowner1991, Sep 9, 2019

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  1. mitsuowner1991

    mitsuowner1991 Proven Member

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    My idle was recently surging. So i did a boost leak test and found a couple major leaks.. so i fixed them and my vacuum sits at 15 like normal.. no more leaks. But my idle is still around 1800 on a cold start in 80*weather and it has a STM BLOCKOFF PLATE installed.. what should i check next.. Somebody gave me a link with things to check when correcting your idle but i cant find the post....


    THANKS AGAIN!!
     

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  2. 91talonts1

    91talonts1 Proven Member

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    1997 Eagle Talon TSi AWD
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  3. jpmxrider489

    jpmxrider489 Proven Member

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    Did you block off the FIAV and the ISC. Those are critical parts on idle. Do you have dsmlink by chance? Check out this link. It talks about properly adjusting the ISC and BISS. They are extremely slow to adjust. On a cold start, 1800 doesn't seem extremely high. When the car is fully warm, what does it idle at?

    https://www.sixsigmatuning.com/pages/dsm-idle-control
     

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  4. mitsuowner1991

    mitsuowner1991 Proven Member

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    When i changed the gasket inbetween the top and bottom of the throttle bodie i notticed the person i bought the car from had a piece of metal over the fiav so i bought the STM TUNES PLATE and installed it.its idleing high with the plate in..
     

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    2005/HONDA/CBR600RR
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    03 Volkswagen Jetta 1.8t
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    1991 Mitsubishi Eclipse GSX
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  5. mitsuowner1991

    mitsuowner1991 Proven Member

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    And i didnt fully let it warm up because i felt that was idleing to high..
     

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  6. mitsuowner1991

    mitsuowner1991 Proven Member

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    The person had TECHNOMOTIVE DATA LOGGER INSTALLED. but i dont have a comp to log it on..
     

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    2005/HONDA/CBR600RR
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    1991 Mitsubishi Eclipse GSX
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  7. mitsuowner1991

    mitsuowner1991 Proven Member

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    This is also installed. And i m havent touched it and i dont really wanna as it ran fine before.
     

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  8. jpmxrider489

    jpmxrider489 Proven Member

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    So you do you have water lines hooked up? Maybe you have the wrong plate? My car idles about that and then drops down to around 1000 once it is warm. Post a picture of your current throttle body as it is on your car.
     

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  9. mitsuowner1991

    mitsuowner1991 Proven Member

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    I still have the water lines.. i used the STM plate to replace the little piece of metal the last owner had in there.. I fell like that 1800 right off the bat is idling hard espacialy since i have the plate. .. i heard when you get the plate youll have to keep your foot on the gas pedal for a couple minutes espacialy in the cold ..
     

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    2005/HONDA/CBR600RR
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    1991 Mitsubishi Eclipse GSX
    16.396 @ 83.38 · 1G DSM

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    1991 Mitsubishi Eclipse GSX
    · 1G DSM
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  10. jpmxrider489

    jpmxrider489 Proven Member

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    Which plate do you have on the car? There are two different ones as you see below. If you have water lines, then your keeping the FIAV. In that case, you shouldn't have to step on the throttle to help the car warm up. When your car is fully warm, what does it idle at? Did you read the link I posted above? There is a bunch of good info in there. If you got the plate that eliminates the ISC, I would recommend using the ISC. Especially if your harness has it. My car idles around there until warm.

    https://stmtuned.com/collections/3000gt-stealth-intake-intercooler/products/stm-fiav-block-off-plate
    https://stmtuned.com/products/stm-fiav-bypass-plate?_pos=1&_sid=200a07ef8&_ss=r
     

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    1995 Eagle Talon TSi
    manual · 2G DSM
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  11. Cherry

    Cherry Proven Member

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    If the plate has holes in it other than the screw holes then the FIAV is blocked and the ISC is still functional. Check the ISC ohm reading and depending on which ISC motor you have (also known as the IAC) it should read 28-33ohms for the stock brown top and if you have one of the black ones it should read 39 ohms. This will tell you if certain things are bad in the motor. You should check the ohms between 1&2 and 2&3 and 4&5 and 5&6. If they dont read then you have a bad motor. If those check out then check to see if the motor acts like it should. Unbolt it the ISC motor but it still plugged in, then reset the ECU by unhooking the battery for 10 seconds and then reconnect it. You will need someone to turn the key for you though since you should see the motor extend all the way out and then come back in slightly.

    Here is a thread showing the 2 processes https://www.dsmtuners.com/threads/dsm-isc-motor-testing-replacement.386663/

    I am currently trying to find how to test the plug from the ECU to the ISC but I cant find any information on it and the Haynes manual is kind of garbage in this department because it just says "one pin should have 12v and the rest should have less than battery voltage" yeah that helps me a lot since I have 2 pins with 12v.
     

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    1991 Mitsubishi Eclipse N/T
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  12. jpmxrider489

    jpmxrider489 Proven Member

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    I have also been wondering about this. I just recently been figuring out about my high idle like the OP and came to the conclusion that my FIAV was stuck. Dsmlink kept my values around 30 and the other value was around 144 as mentioned in the link I posted above. Seems after I adjusted it and thought it was dialed in, after restarting the car a day later, the values have a mind of its own. If you are wondering about the ISC being bad from the ECU, maybe take off the ecu cover to see if its leaking? Thats all the info I have found over time.
     

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    1995 Eagle Talon TSi
    manual · 2G DSM
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  13. Cherry

    Cherry Proven Member

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    I had gotten an ECU from Steve on here that had some ones that he rebuilt for an N/A laying around since the people at ECMLink never replied back to me. BUT, they say if the ISC is good to check the ECU drivers being blown, which I could open mine up again to check but I highly doubt it since I opened it when I got it and it looked spotless (doesnt mean something couldnt have failed since then but I have hardly ran it) and then they say it could be a wire between the ECU and ISC motor but how to test it, how to see if you are getting correct voltages or whatever else since I have 2 reading 12v (Haynes says only 1 but if you look they are using a 90 and everything change in 91 you can see they are probing the ISC pigtail from a 90) pin 2&5 which when you test the ISC motor with a 6v battery you are supposed to jump 2&5 and 3&6 to check for movement.

    I guess the only thing I can do at this point is look up the ECU pinout and test continuity from there to the plug. I would guess if the motor isnt being told to move the voltages wont be present but the other pins 1,3,4&6 are probably grounds the ECU uses to manipulate the motor.
     

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  14. Cherry

    Cherry Proven Member

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    If it is the FIAV housing for you and you have link, I would pop the freeze plug out, twist that thing in, possibly put some RTV around it and close it back up and then set link to simulate the FIAV with the ISC. The ISC and the FIAV work together in the first place. Also learned what causes idle surge by reading ECM link. While it is caused by too much air bypassing the throttle plate, the surge comes from an idle lock set in the ECU, when it goes over that point it cuts the injectors off until the rpm comes down, when it does it enables the injectors again and then it becomes a cycle of cutting fuel and turning it on. If you have idle surge then you have a leak somewhere. If it doesnt show up in a boost leak test then it could be the FIAV stuck open, bad ISC, throttle plate not adjusted properly or even the coolant temperature sensor being faulty. The ECU reads a cold engine, opens the ISC port more causing the idle to go up and if it reaches the point where it gets to the idle lock then you get idle surge as well from my research on here.

    BUT, looking at the plug at least for a post 90 pre 95 model the plug should have power going to 2&5 and the rest read 0 for me and it looked like the ISC is working properly. I found the difference between the Turbo ISC and the N/A ISC from parts stores though, while both do work, the N/A one looks like an actual Mitsubishi part, has a Mitsubishi logo on it with a few numbers while the Turbo ones that I got have no markings other than like a 5 digit part number on it.

    That looks like where the cost difference is coming from at parts stores.
     

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  15. jpmxrider489

    jpmxrider489 Proven Member

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    In my case I believe it is stuck open because of it not showing on my boost leak test. And I have tried popping the freeze plug out on two other throttle bodies I had and both times the plastic piece was froze or breaks when turning. In my case I was best to just eliminate the issue since my car is driven under 30 times a year.

    However the OP must if solved his issue because no response.
     

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  16. Cherry

    Cherry Proven Member

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    A new FIAV housing is 140 dollars if I remember correctly, probably not worth it however if you drive it so little. If you do get one though look under a 3000gt vr4. Thats the only place i was able to find it.

    If the throttle plate is out of adjustment it can cause issues as well. Mine was at least 3 turns out of adjustment, throttle cable was too tight, BISS was broken and stuck in the throttle body which is why the throttle plate was out of adjustment, leaks galore, timing was off by like 17 degrees where it was 12 degrees ATDC. Gotta love hacks out there and trying to find all the stuff they messed up. My 1.8 had oil leaks but it was never this frustrating.
     

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  17. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Has the OP checked the tension on the throttle cable and the throttle stop switch/bolt? It could be one of those holding the idle up high.
     

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  18. mitsuowner1991

    mitsuowner1991 Proven Member

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    I did adjusted the cable as the SIX SIGMA GUIDE states to. When adjusting my TPS i have it at 0.49 closed and when opening i know it should go close to 5v but with mine WOT it gos wayyy past 5volts.. Could the TPS be bad.. The car idled bettèr and correct when the throttle boddie was full with dried collant
     

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  19. mitsuowner1991

    mitsuowner1991 Proven Member

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    I didnt know anybody replied to this.. i recently noticed my coolant keeps going low and that is was leaking from some of the sensors on the coolant flange housing. Amd i tested the coolant sensor and matched it to the specifcations in the chiltons book and its way off meaning its bad. The continuity is suppose to read between 2.21 - 2.69 kohms in 68*f water. So i did that and was getting a reading of 1.35... so it says it should go up with hotter water and mine barley moves. So i ordered all new stuff.. will let you know..
     

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    03 Volkswagen Jetta 1.8t
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    1991 Mitsubishi Eclipse GSX
    · 1G DSM
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  20. Cherry

    Cherry Proven Member

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    There is several things that go into idle and trying to find what is going on is the hardest part.
     

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  21. mitsuowner1991

    mitsuowner1991 Proven Member

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    My idle was fine even with the vacuum leak.. then i took the TB off and cleaned it out real good and put the TPS back on and adjusted it. Now when i cold start it revs up for a quick second then drops into the idle surge...and the vacuum leak is fixed. Lol frustrated and im running out of time before winter.. ughh
     

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    03 Volkswagen Jetta 1.8t
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    16.396 @ 83.38 · 1G DSM

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    1991 Mitsubishi Eclipse GSX
    · 1G DSM
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