yep sounds like hose. Especially check all hoses attached to the intake hose. Those cause huge idle issues if disconnected.

 

agree with guru and ej257gd.

Went to the dealer and the tech fixed and told me the line from the fuel pressure regulator to intake manifold was loose.

 

I just bought an 08 MR (40K miles) and now out of nowhere I find the idle sometimes goes up to ~1.5K. First time I test drove I noticed it but just slightly since it went away after a while. I took my mechanic to the dealership to check it out and the car never did it that time. The mechanic ran the scanner (since it has the CEL ON) and problem turned out to be the O2 sensor heater. From modification I can notice so far the car has the AEM Intake, Borla Catback, ETS Intercooler Piping Kit (Still not sure if intercooler was changed or just piping). Not sure if the computer was flashed.

Does anybody know what could be wrong?!

 

Two year old thread but I'll bite.

Be sure to zip tie that sucker on there. It will happen again otherwise and typically happens over 25psi.

If you haven't already change the fuel pump relay, they were all the bad ones in 2008 and with 40k miles I'd assume it will need changing even if it already has been. It's a $30 part and Mitsu will know what you're talking about or you can pick one up from AMS online.

Check the fuel pressure regulator hose where it connects to the front of the engine on the passenger side (what this thread was about) make sure it's firmly attached and zip tied on.

what p code was actually thrown that caused the CEL? Was the idle higher only when the motor was cold? If so, that's normal.

If it has the AEM Intake and doesn't have a tune it could be running lean. The 08's were tuned super rich from the factory so it might be okay but better to know for sure and invest in a wideband AFR gauge or get a pro-tune somwhere. Catted or test pipe? You can tell if it has an upgraded intercooler by looking at a factory one vs yours and see if yours is thicker/bigger bar/plate, gap between front of it and back of front bumper.

 

Thanks for all the info. I'll definitely check on the relay and hose, and I was already planning to invest in a AFR already so good to know that it will be worth it. On the intercooler, I only had the chance of spending an hour with the car before heading back for work away from home for a few weeks. (My wife has driven it more than I have ) Thanks for all your help

 

i had one with a cold air intake and would idle real stupid when fan kicked on engine would take in hot air from radiator...put a plate made for this and stopped it.... there is another flash for this that came out for this a couple of months back.