My wife's '96 2.6l TS auto (220,000 kms) has similar problems to other rough idle faults on this site but I would describe the symptoms a little differently.

In my case the motor idles great hot or cold at the correct 800 rpm setting in neutral, turning the air con on hardly affects the idle speed and when the radiator fans come on there is only a minor drop in revs - all appears normal. Also there is no cam chain rattle when hot or cold.

Anyway, shift the auto into Reverse or Drive and the revs immediately drop approx 150 rpm to around 650 rpm and the rough idle symptoms begin with steering wheel shakes .

When driving the roughness is still there until the revs get to around 1500 rpm and then everything smoothes out and the car runs beautifully. Fuel consumption seems reasonable at around 10 kpl for a mixture of city and freeway driving.

I've checked all the sensors around the engine including the TPS, ISC, ignition timing, plugs, ignition leads, checked all connectors, removed power and reset the ECU, checked the ECU codes, etc - everything that I can think of but nothing seems to work. BTW I have an electronics background.

Could this be an auto transmission fault and not an engine fault?

Is it possible to read the TCU fault codes like you can with the ECU fault codes?

I have a Haynes manual and all it says is take it to a dealer.

Hello dero,

Here's how you pull the fault codes on a '92 US Diamante.
http://www.diamanteowners.com/forum/index.php?showtopic=64648

and here's the location of the '92 Diamante TCU
http://www.diamanteowners.com/forum/index.php?showtopic=62534

Hope this helps

TG

Hello dero,

Here's how you pull the fault codes on a '92 US Diamante.
http://www.diamanteowners.com/forum/index.php?showtopic=64648

and here's the location of the '92 Diamante TCU
http://www.diamanteowners.com/forum/index.php?showtopic=62534

Hope this helps TG

Excellent :D TG, thanks heaps - mate your blood's worth bottling :D this will help heaps.

I've been searching high and low for that sort of info for ages. I haven't solved the problem yet but now at last I have found a way of proving whether the auto transmission is the problem.

Like I said TG, I'm stoked, thanks again

Hope it gets fixed soon!
Let us know what happened :confused:

This topic has been covered many times and usually is not one problem.

Even for 1st/2nd/3rd gens they all often have this problem.


Id suggest looking at the TPS and see'ing if it has a build up of cr*p on it.


Otherwise do a search theres a huge list of things.


good luck

Hello dero,

Gald the information was useful.

Some additional information on the ISC from ECM ToGo - reputible rebuilder here in the U.S. for ECUs. http://www.ecmtogo.com/

"Mitsubishi ISC (idle speed control/servo) Motors

Mitsubishi ISC motors can fail and cause irreparable failure to the ECM. Most Dealerships as well as our technicians recommend replacing your ISC when the ECM engine control computer is repaired or replaced.

Symptoms of failing ISC control motor include: idle surge, failure to idle up on cold start, idle oscillation with engine idle revving up & back between approximately 900 to 1500 rpm's at idle (which should be around 850 with engine at operating temperature) or an unresponsive high or low idle. The car should compensate and idle up when the a/c compressor, power steering or when fan is running. It's likely you'll need to replace this at some point in your Mitsubishi.

Replacement of ISC and ECM does not guarantee your troubles are over. Check complete ignition & electrical systems before reinserting your ECM unit. Many times our technicians can tell by the damage on the ECM motherboard if the ISC was likely to have caused the damage. The unwritten rule with DSM Mitsubishi's is to replace ISC with ECM or between 50,000-75,000 miles."

Omg i think you have answered my question...

Your a gem
Thanks mate!

Ummm any idea on how much this costs to replace?

Here is some more useful information on the ISC / IAC motor.

TG

http://www.stealth316.com/2-isc-iac.htm

Omg i think you have answered my question...

Your a gem
Thanks mate!

Ummm any idea on how much this costs to replace?

Hello dimi108,

I'm not sure of the price ECM ToGo charges to rebuild the ISC. You can go to their website and email them. This would be in dollars($) and you could convert it to AUS dollars to get an idea of the price. Or call you local dealer ($$$$$$$$ !!).

TG

Here's some more information on the ISC - romiving and testing it.

TG

http://www.crebotech.com/page2.html

Well I'm really learning heaps about Magnas this past couple of years, I drive a TH (3.5), my wife has a TS (2.6) and my son has a TF (2.4). For the past 10 or 15 years I've really liked Magnas especially the TH shape and so when I got the TH I also got a TS for the wife - big mistake.

Having owning 8 new Mazdas throughout my life with mileages ranging from 120,000 kms through to 260,000 kms before selling I've come to expect my cars to be reliable - until now. In something like 1/2 million kms of Mazdas I never had a complete breakdown, 2 minor breakdowns (still driveable) and only minor things like thermostats and belts.

But with my Magnas I've had engine mounts @ 80,000 kms, valve stem seals @ 150,000 kms, drive shafts, batteries, expensive rough idle problems, brakes and heaps of other assorted problems - any chance there ever was of me buying a 380 in June this year is fading extremely rapidly.

I think it is going to be bye bye Mitsubishi very very soon, I've had enough.