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
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.
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).
"... 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.
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
about carbon deposits: probably they affects also the ISC throttle,
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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