just bought an 03 evo8 and it has a terrible idle. either idles too high or i cant keep it running. i bought a brand new stepper motor from mitsbishi part number being 1450a069 and right away when opening the new part and comparing it to the old part there is an obvious length difference in the metering needle. still went ahead and installed it and it had a crazy high idle and even when i did an idle relearn it did nothing. now Ive googled part number and it will actually pull pictures of both parts (mine and the new one). has anyone else had this problem and what can i do? cus the new one obviously isnt going to work

 

If the car utilizes a MAF sensor ( most likely ), I'd check for boost leaks.

 

im not doubting you at all but why would it do that? would it act like a vacuum leak at idle because youre not building boost? and it does have an aftermarket Injen MAF think that could cause it??

 

The early evo 8's utilized a rubber coated iac valve and that design was deemed to be flawed so it was replaced on the '05 8's and the '06 9's with a hard plastic plunger that is surrounded by a stiff spring. Does this sound familiar to you? The newer version will still work with your '03 and again is an improved design. There's nothing wrong with your iac valve and I agree with the previous poster about a vaccum leak.

 

I would be willing to bet its the IACV. Find a used 9 one for cheap and I bet that fixes it. Have you tried adjusting the idle with that thing with 2 bolts on the throttle body. dont remember what its called, but it has two bolts and you loosen them and slide it while the car is fully warm.

 

No problem, I suppose I used the incorrect terminology.. but I mentioned "Boost" because the easiest way to test your system for air leaks is to perform a "boost" leak test.

The problem is that, when using a MAF, all the air behind your MAF is metered air.. so your engine expects to get that amount of air no matter what. If you have a leak past the MAF then yes you have a vacuum leak and the motor gets confused, causing idles to fluctuate.

Do a boost leak test / leak down test on your air system before you go out and purchase any unnecessary parts.

 

Yeah I still agree that it is a boost leak. Also the iac valve has a seal on it that is a pain in the *** to seal up. When I had my car at strictly modified last time they couldn't get my iac to stop leaking air past that weird little flat oring seal on it. They eventually put a small bead of rtv on the throttle body where the iac connects to it and that finally sealed it up and no more boost leak there. If you are using an after market iac then the chances that it is leaking is even greater as I have had better success with the oem oring and piece. Good luck but I bet its leaking at the iac where you changed it.