Mitsubishi 1.8 GDi

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Mon 13 Feb 2006 20:21
Mitsubishi 1.8 GDi - JustMike
Good evening wise and knowledge-able friends and a good evening too to those others like me who are neither wise nor knowledge-able!
My problem today is with my sons much loved Mitsubishi Carisma of 1999 vintage which has a 1.8 gasoline Direct Injection engine which has done 70k miles,performs well and has been economical for the past year.
It has now started to run "fast" on tickover - about 1200 rpm instead of its usual 750 and sometimes surges briefly when slowing down for road junctions/ roundabouts etc.

It seems as though it is the "choke " which is stuck slightly on and it smells very benziny near the exhaust - as though it is running rich.

The throttle cable is not sticking and removing the air filter makes no difference.

There are two fuse boxes - one under the bonnet and another in front of the drivers knees behind the dash. I cant see a diagnostic plug/socket near either of them but I know it must be somewhere !!
My friend will plug his all knowing laptop in for me if I can find the socket.

If anybody can tell me where the plug is I would appreciate it or better still if you have any ideas of what the problem is or how to cure it with a big hammer and a set of open ended spanners I would be delighted.
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Mon 13 Feb 2006 21:07
Mitsubishi 1.8 GDi - Aprilia
16-pin DLC is under the dash (roughly under the steering column area).
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Mon 13 Feb 2006 22:58
Mitsubishi 1.8 GDi - JustMike
Thanks for that. I have read the other current topic about carbon build up on GDI engines - it makes intersting reading !!
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Mon 13 Feb 2006 23:10
Mitsubishi 1.8 GDi - Aprilia
Yes, you may have a problem with carbon. Unstable idle is one of the symptoms.
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Wed 22 Feb 2006 23:35
Mitsubishi 1.8 GDi - JustMike
Thanks.
Where is the carbon likely to be? Does its presence fog the ECU's brain re tickover speeds ?

Its now up to 1500 rpm on tickover sometimes - but starts and runs fine. I have tried carb cleaner down the air intake but to no avail.
Is there a "snake oil" remedy or will I have to wait until Christmas and save all our walnut shells to ram down the air intake.?
Will an Italian tune up make any difference or just risk getting more points ?
If it were an old type engine I would think it was part of the carb sticking in its guide (eg SU slide) but I suspect its more technical than that- I would love to fix it though just to impress the offspring.
I remember when car makers and others used the KISS system -Keep it simple Stupid... That, I could cope with.
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Thu 23 Feb 2006 07:49
Mitsubishi 1.8 GDi - Collos25
We suffered exactly the same symptoms on Fiat recently it was diagnosed as the stepper motor a common fault high revs at tickover and thens runs perfect.The solution was in fact a sensor failure which sends info to the stepper motor making it think the engine was always cold so it increases the revs.
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Thu 23 Feb 2006 10:45
Mitsubishi 1.8 GDi - Aprilia
Yes, it could indeed be the idle air valve motor or the coolant temp sensor. With the appropriate diagnostic tool you can read live data and check this out.
On Mitsi's, when the idle valve goes bad it usually stops working completely (there are two windings and one fails) - if you can use a DMM you can check the windings to see if one has gone open circuit (infinite resistance). They are usually about 50-ohms IIRC.
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