uneven idle speed on Mitsubishi Eclipse 2.0 m.y.1991

Hi, I have the a.m. car, I changed both ECM and ISC but the idle speed is still uneven, especially when the cooling fan and the air conditioner
are running together.
Might it be poor battery condition, or air intake control failure, or what?
Andrea
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Could be a vacuum leak, could be carbon (crap) built up in the throttle. Check and replace faulty vacuum lines. There is a sticker on your hood that maps all of the lines. Go to a Chrysler/Dodge/Jeep dealer and buy two cans of M.C.C.C. (Mopar combustion chamber cleaner) for $6.00 each. Slowly spray the entire contents of the two cans into your air intake somewhere between the turbo and throttle body while the motor is running. Observe the stinky plume belching out of your tailpipe and politely smile as your neighbors complain (my favorite part!) This stuff will remove carbon and clean the top end of the motor which seems to get fouled due to the EGR system. It really does work and is a favorite among the DSM crowd.
The uneven idle is caused by the ECU advancing and retarding ignition time, trying to keep idle at the 750rpm set point. You've either got a leak that's allowing unmetered air in or a blockage that's preventing the ISC from being able to control idle air.

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simpleton ha scritto:

I'll do it right today, but the question is: why carbon builds up in the throttle? please note that my engine is non-turbo.

I changed the faulty ISC and ECU/ECM 4 months ago with upgraded units. But, I have to point out that my car is LPG fueled (in Italy is very popular to use LPG as fuel because it's cheaper, saving 30% off, and keeps the car performances). This way, between the air intake control and the throttle there is the gas injector, which probably affects the ISC unit running. Nevertheless, other cars with this system have a smooth idle speed, it depends on the different way for idle speed control. This Mitsu ISC is damn complicated and faulty. When the car is turned to gasoline fuel, the situation is better (but not definitely right).
Thank you! Andrea
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"... but the question is: why carbon builds up in the throttle? please note that my engine is non-turbo."
The exhaust gas recirculation system re-routes a portion of the exhaust gas through a port in the head and back into the intake manifold.
What system do you use to control the air to fuel ratio? A lean condition could also cause idle instability.
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simpleton ha scritto:

usually the LPG fueling systems have a emulator of lambda control and an interface to ECM unit, so the system works the same way as the gasoline one.
as obvious, my shop checks the good air to fuel ratio also with exhaust gas analysis.
about carbon deposits: probably they affects also the ISC throttle, isn't it?
thank you! andrea
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Andrea, carbon deposits , although possible are much less likely with lpg.
Have you been able to examine for leaks? The Biss screw and throttle shaft seals are both known to leak at times.

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simpleton ha scritto:

sorry, what's biss?
thank you again!
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Base Idle Speed Screw (biss)
It is the air bleed screw in the throttle body that allows for adjustment of idle. The o-ring that seals it tends to rot and allow air to leak.

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simpleton ha scritto:

The workshop chede it out, and found a bad camshaft position control: when some electri device is on, e.g. the air conditioner, the unit sounds as sparkling. now I'm going to make it cleaned by an electric workshop, but hope that this fixing will be final..
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http://www.ecanfix.com/~manualcd/gift/dsm/1g-90-92-4g63overhaul.pdf
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