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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8538
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi Diamante LS: I have a 2003 Diamante. It does not

Customer Question

I have a 2003 Diamante. It does not seems to be idling up when you turn the ac on or when you put it in gear. I just replaced the tps and still have the same problem. Any suggestions?
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.
Hi,
Is it the TPS you replaced or the IAC (idle air control) valve? The IAC is what is responsible for idle-up operation.
Customer: replied 1 year ago.
It was the TPS. Is there a way to test or clean the IAC valve before replacing it?
Expert:  Doug replied 1 year ago.
Thanks... we definitely need to look into that IAC then.
When you turn the AC on, there is definitely no idle-up before the compressor kicks on right?
What about if you pull the steering wheel hard to one direction and hold it... does the idle go up or go down when the steering load is added?
Customer: replied 1 year ago.
Correct. No idle up when ac is turned on. Also, when I pull the steering hard to one direction and hold it there is no change in the idle. Also I meant to mention that when we are at a stop light it will shut off unless we hold the brake with one foot and give it a little gas.
Expert:  Doug replied 1 year ago.
Thanks.
The stop light issue can sometimes be just a dirty throttle, however with no idle up occurring we know that issue takes precedence over it as it could affect both conditions.
Lets go to the IAC and check it out. You'll need to take the intake duct off then the IAC is held on with three screws directly below the throttle opening.
Take it off and clean it, then use your fingers to gently but steadily force the pintle closed. Reinstall the IAC and see if your engine revs high and does not drop normally.
Customer: replied 1 year ago.
Ok. I took it out but I am unable to push the pintle closed.
Expert:  Doug replied 1 year ago.
Thanks.
If you are unable to push it in that is a pretty good indication that it is frozen. While not "easy" to push in, with steady force and at most a little wiggling it should go in. If it can't go in for you, it likely can not go in for the computer either... your hands provide a lot more force than the tiny electric motor inside it.
Before doing anything else lets get a new IAC in there. Take the opportunity while it is out to clean the passageways and the throttle opening, then get the new one in there. Short of anything REALLY unusual like a computer or wiring failure, this should take care of you. Not being able to move it by hand just further seals the odds.
Customer: replied 1 year ago.
New TPS and new IAC. Still having the same issue. What do I try next?
Expert:  Doug replied 1 year ago.
Just to be clear, the throttle is clean, the IAC is new, and the key problem is that you are not seeing any idle up under load or when stopping etc? If that is correct, the problem did not change in any respect at all, right?
Was there anything abnormal about the connector to the IAC? Was the IAC new or used? If new, was it from a respected brand?
Customer: replied 1 year ago.
That is correct. Nothing has changed. Connectors looked fine. The IAC was new. The brand was BWD.
Customer: replied 1 year ago.
Cleaning the throttle was the very first thing I did.
Expert:  Doug replied 1 year ago.
Hmm.
Lets pull the IAC out but leave it plugged in. Have a helper turn the key on (but not start the engine). Can you feel the IAC hum and move slightly? If not, turn the key off and move the pintle out all the way by hand then turn the key on again, does the pintle retract?
Customer: replied 1 year ago.
Just followed those instructions. It did move out slightly when turned on and retracted when turned off.
Expert:  Doug replied 1 year ago.
Thanks, ***** ***** is working then.
Are you sure there isn't anything else worth mentioning about the situation, like someone modifying the throttle stops trying to "fix" the situation previously etc?
Customer: replied 1 year ago.
We put a simple code reader on the vehicle and saw codes 101, 401 and 403. We. We also used MAF cleaner and cleaned the MAF even though it did not appear dirty.
Expert:  Doug replied 1 year ago.
None of those codes would have anything to do with idle up not working. Seeing as the iac is working outside of the throttle, let's put it back together and recheck operation... It should be idling up now.
Customer: replied 1 year ago.
Everything is back together and there has been no change in operation.
Expert:  Doug replied 1 year ago.
There really isn't any reason that should be unless something is being left out. The idle up is performed by the iac which is now working and no longer seized. The idle up is commanded when the ac or the power steering is used and neither is causing it to work... Making it unlikely to be signal related since there are two separate unrelated signals and neither would be working.
You know the wiring is okay as again it is verified working.
You could expect a computer failure to cause this, particularly knowing the old iac was seized, however again the iac is verified working meaning the computer is doing its job.
Again with the idle up specifically there really isn't anything else to consider. While you can have other problems cause similar drivability issues, the actual idle up process is extremely narrow in operation, and everything is checking out.
What I would have to do at this point would be to get the throttle body calibrated as all I can imagine is someone tinkered with it trying to fix a problem in the past perhaps. Any shop with a professional grade scan tool can do this by activating the SAS or base idle function, then dialing in the idle while the function is active.
If there is still issue while everything is calibrated I really wouldn't have anything else to suspect but a very strange and very unusual computer problem.

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