FKD up Idle. Advice Mike?

[evolved_st8]

Mike. For the last week my car has been doin funny stuff. Havent changed anything but the Idle sux. What it was doing at first was cutting off when decelerating to a stop. Now its idling high. It changes from 1300 -1800 over and over. Sounds almost like when the evo first came out and cams were installed. Not really a lope just a consistant idle change. Any ideas? Something wrong w/ the tune?

[Skiracer]

try pulling the negative battery off for about 10 minutes to reset the ECU. Then reconnect it and let the car run until the radiator fan kicks on twice. Shut off the car, then restart again and hopefully the idle is back to normal... May/may not work, but its something simple to try.

[EvoVIIIGSR]

also....i'd check for any loose vaccum lines.

[blkside]

Yeah.. sounds like the engine is hunting so I would check vacuum lines and also.. stop blocking the sun darkness..

[evolved_st8]

Yeah.. sounds like the engine is hunting so I would check vacuum lines and also.. stop blocking the sun darkness..


Dont u have some terrorist to shoot or somethin? Get the hell on then.

[Mike W]

For an EVO to idle high, air needs to be getting past the closed throttle plate.

Air can go past by:

Throttle plate not closed all the way Cable can be holding it open. Something caught in the linkage at the TB, a dew rag got sucked in and is hanging it open...

BISS Base Idle Set Screw The little screw in the little chimney thingy on the top rear of the throttle body. If it is out too far, idle goes up. If the o-ring that keeps it from moving is all baked out, then it can migrate on its own. If the idle is ever too high or too low, a good So Cal EVO member would always adjust the screw first before running to the nearest message board to post about an idle issue.

ISC - Idle Speed Controller The ISC is a little stepper motor controlled servo that also can let the air around the throttle body. Its job is to raise idle on warm up, higher alternator loads, power steering loads, and maintain a steady idle. When the ECU sees a closed throttle, it takes over control of the idle and uses the ISC to do it.

It might be too open because it is a) dead electronically, one of the four stepper motor coils is burnt out. b) it is all gummed up and cant move like it wants to c) Maybe it is working fine but the ECU is whacked. It is a couple hundred dollar part.

FIAV - Fast Idle Air Valve A thremo valve built into the throttle body. When the throttle body is cold it is open to allow more air in. When the throttle body is hotter it is closed to allow no air in. If this gets stuck or lazy, it can cause a high idle. THe ISC alone can not allow enough air in on a cold start to keep the idle high. This valve assists the ISC in keeping a high idle on cold starts. It is not computer controlled though.

Boost/Vacuum Leak A loose hose or bad gasket can let air in. We are seeing more hoses back by the EGR valve loose.

If the ECU sees a closed throttle and RPM over a certain amount, it will cut fuel. This can cause some serious idle surging. From here (my keyboard) I have no way of telling which one of the above you might have going on. Start with the set screw. Check vacuum hoses next. If it is still suckey, stop by.

Mike W

[evolved_st8]

looks like the plugs are fouled mike. How would that happen in 5k miles? I checked a few of your other suggestions. looks fine. The engine stopped hunting but plugs are definately gone.

[Mike W]

Then either:

The correct amount of fuel is being injected, but for some reason it is not getting burned completely. Low compression will do this. Weak spark also can cause that.

Or:

Too much fuel is being injected and the correct compression and good spark cannot light it off.

Clean or replace the plugs and see if the problem remains or goes away.

Mike W

[HB Evo Owner]

would also like to know whats wrong with your car, my car has the same exact symptoms and when i checked my plugs a week or so b4 this problem happened they were okay still..

if its the plugs on yours i will try new plugs in mine also..

[Mister]

I'm having the same idle issues.....
I hate troubleshooting.....

[RALLInspired]

most of the evos have an issue with the BISS screw as Mike mentioned above... it helps if you have EvoScan and use the BISS actuator to temporarily disable the ECU from trying to adjust the idle on its own and allows you to set the idle more precisely by adjusting that screw. its not a definate answer but the most common and easy to fix. O0

[HB Evo Owner]

ive been having the same problem. just seeing what the OP's problem ended up being.

i do feel that possibly theres some sort of air/vaccum problem or spark.

car idles high, then will suddenly drop and try to die, sometimes it will...sometimes it wont.

sometimes there is throttle lag and other times there isnt.

[Mike W]

I didnt see the OP post up cause or a solution.

Mike W

[evolved_st8]

plugs werent completely fouled. But were fouling fast. Bought new plugs last night. Ran a compression test. Was told that its within range. Im guessing too much fuel. I keep throwing a P0172 error code too. Scot said he'd look @ it thursday. no worries. thx for ur help mike. and the rest of u guys. see u tomorrow night mike.

[jamesinger]

so what is the final verdict?