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348 idle issue and questions

Discussion in '348/355' started by Dino L, Nov 10, 2018.

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  1. Dino L

    Dino L Rookie
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    Oct 29, 2018
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    sacramento, ca
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    William D Lozano
    Recently my 89TS has been staying at a high idle.1200 +/- and occasionally it seems to be searching for idle once it is warmed up. It jumps back and forth 800/1200 rpm then will eventually settle back at 1200 which I know is too high. I suspect there must be a sensor to know it has come to temp and should drop the idle and I am suspecting this is also the cause of the idle searching ? Temp is about 195 and fans do come on. Thanks in advance.
     
  2. Wade

    Wade Two Time F1 World Champ
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    Mar 31, 2006
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    Any recent work in the engine bay?
     
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  3. Dino L

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    Most recently a coolant flush and coolant hoses replaced. Before that, and possibly when idle issue was first noticed, a coil pack and cat temp sensor.
     
  4. Cauf61

    Cauf61 Formula Junior
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    Jul 12, 2016
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    Did you perform a search for air intake leaks. Easy with brake cleaner. Just spray a bit on all tubes/lines and engine will react very fast when a leak is found.

    Attention for fire with brake cleaner on hot parts ( exhaust ) !!
    Keep extinguisher at hand.
     
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  5. ernie

    ernie Two Time F1 World Champ
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    Nov 19, 2001
    21,918
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    The Bad Guy
    1) Your throttle bodies need cleaning.
    Dirty build up inside the throttle can cause the plate to get stuck against the inner wall. So make sure your throttle bodies are cleaned out properly.

    2) Your throttle stops are not adjusted properly.
    If one of your throttle bodies hits the stop before the other it can cause one of the throttles to say open just enough for it to idle higher than normal. Check to make sure that both throttle bodies are

    3) The throttle linkage is not even
    Same as above. If the linkage is not opening and closing the throttles in sync you can have one throttle saying open more than the other. So make sure that the throttle are opening and closing as synchronous as possible.

    4) You throttles are not balanced.
    To balance the throttles it is best to use a manometer. Look up on YouTube how to make one for a few bucks.

    5) Dirty idle air control valves.
    If you idle air control valves are dirty they can get stuck and not fully close. So clean them out. Look in the 348 DIY sticky on how to clean the IACV.

    6) The "secret cruise control".
    Basically make sure that your floor mat is not bunched up against the gas peddle. It has been know to happen. Also make sure that there isn't any debris under the gas peddle stop causing it to stay open a hair.

    7) Motronic ecu reset.
    Every once in a while it's a good idea to disconnect the battery and let the ECUs relearn the warm up parameters. What happens is the Moronic ECUs use the resistance of the throttle position sensors to determine where the throttles are (but in your case the throttle as the '89s 2.5 Motronic only has 1 tps), and then it uses that info to adjust the fuel mixture and the idle parameters. To reset them, disconnect the battery for 30 seconds, reconnect the battery, make sure ALL accessories are turned OFF, start the car, let it idle for 15-20 minutes or until the radiator fans kick on, then take it for a 30 minute drive.

    Try those and get back to use. We like updates. ;)
     
  6. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
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    That's a bit harsh calling them moronic, isn't it, Ernie? :p
     
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  7. Dino L

    Dino L Rookie
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    Thank you I will give this a look on the weekend
     
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  8. Dino L

    Dino L Rookie
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    Thank you for all this very good information.Some of this I can handle myself and if those don't resolve I will take it in to the expert.
     
  9. Dino L

    Dino L Rookie
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  10. Dino L

    Dino L Rookie
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    Thank you I will give this a try on the weekend.
     
  11. Dino L

    Dino L Rookie
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  12. Dino L

    Dino L Rookie
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    Thank you I for all the great info. I will be spending some time on this over the weekend and hopefully be able to post a resolution.
     
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  13. ernie

    ernie Two Time F1 World Champ
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    LOL!
    Gotta love auto spell check.

    Well they are a bit "moronic". The Motronic ecu may have gotten the job done in the late '80s early '90s but they are not up to snuff for modern day requirements. Trying to run the Motronic today for performance modifications would be like trying to still use a Commodore64 to run Windows 10 = moronic. :p :D
     
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  14. ernie

    ernie Two Time F1 World Champ
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    Be sure to look in the 348 DIY sticky for how-to's, and search the archives. Practically everything I posted has already been discussed.
     
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  15. Koenig1

    Koenig1 Karting

    Aug 25, 2016
    247
    Ottawa ON
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    Sandy
    I'll add one more possibility. I purchased mine with a high idle, spent a couple of months looking for a leaky hose, throttle adjustments, pedal, etc. Finally I left it as I knew I needed to do an engine out, and would be much easier to diagnose. The killer was the left intake cam had jumped a tooth! Anyway, when the engine went back in, it idled at 1k rpm. The PO probably knew this but..., welcome to private sales! Hope this is not the case for you. My car's PO was not very honest regarding a number of issues... but probably typical of his demeanor. My gut said no, my heart won out!
     
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  16. Dino L

    Dino L Rookie
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  17. Dino L

    Dino L Rookie
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    Thanks... I am hoping it is not that serious, but always a possibility. I had the engine out major completed about 4 years ago, and I am planning for it again this spring. Like you, my first engine out came with a few surprises, but I feel good that they were found and resolved.
     
  18. Dino L

    Dino L Rookie
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    Idle issue appears to be finally resolved after several items addressed. Connections at MAS were carefully cleaned and inspected. New (used) CAT's installed. Ran a tank of Hi octane race fuel thru it. I have now been thru 4 tanks of fuel and numerous outings with the car and not a sputter. Idle goes right to about 1100 each and every time off the gas.
     
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  19. ernie

    ernie Two Time F1 World Champ
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    Your idle is still a hair high, it should settle down to around 950. You may need to adjust the throttle stops and/or adjust the idle bypass screws.
     
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