High Idle When Warm

[iceminion]

Originally Posted by mnim15

Just curious, how does the circuitry on the ECU get damaged?

when the IAC fails, the ecu does not know that it fails. The ecu continues to "tell" the IAC to open more and more, the IAC does not respond to the voltage inputs. Eventually the (abnormally) large amount of resistance inside the IAC causes the drivers on the ECU board to fail. Contact someone at ecmtuning.com for a more detailed description

[iceminion]

Originally Posted by AwdGSX13

lots of reasons, caps can leak and mess it up...

No, not in the context of what we are talking about, leaking caps will cause:
-Check engine
-bad running -and- bad idle
-"fishy smell"
-physical visual damage to the board.

The damage caused by a bad IAC does not match any of the above criteria.

The only real way to see if you have a bad IAC/IAC board drivers is to take the car out of gear while rolling, RPMs should be about 900-1300. When you come to a stop, the IAC should drop the RPMS down several hundred to about 750RPM.

One of the ECUs I tested worked great and the car idled pretty well, but using this test the car almost died when I let off the gas and applied brakes, and in the best case it would go down to about 700rpm when rolling, which is not correct and dangerous.

[1QUICK4]

Originally Posted by iceminion

The FIAV is great, it causes the engine to warm up faster, so your engine will last longer. Cold pistons = piston slap.

The FIAV does not "warm up your engine faster" as you put it. All it does is bump your cold idle up a bit.

The engine coolant warms up from the heat from the combustion process, not from routing coolant to the throttle body.

[Goat Blower]

Yeah, all the FIAV does is allow more air around the throttle plate for a higher initial idle, which in turns warms up the car slightly faster. When the coolant warms up, it melts the wax pellet in the FIAV which blocks off that air passage and lowers the idle.

And cold pistons don't equal piston slap. Stock pistons are cast which expand very little compared to certain types of aftermarket pistons, so piston to wall clearance is tight so you're not getting piston slap. Plus pin offset and the skirts also guard against the piston rocking at all in the bore. You get initial piston slap with brands like J&E or all out race pistons because they're made from a tougher alloy, 2XXX something while most street/strip pistons like Wiseco's are made from a slightly softer alloy, 4XXX something which has less tensile strength but also doesn't expand and contract as much as the 2XXX something alloy, which requires a lot of wall clearance for expansion.

[xveganxcowboyx]

Piston slap is a bit of a concern for me given that I have a 2.3, but not enough to make me put all the ugly mess that is the lower half of the throttlebody back in.

Just a small update. I decided the most pressing issue was to get my exhaust fitment correct. While swapping engines I also changed my O2 housing (LIPP). The exhaust did not bolt up correctly and my O2 sensor was moved to the bottom of the O2 housing so it was reading a lot of outside air. On top of that, my wideband was completely inaccurate. I have so far only had time to fix the exhaust (and now the wideband is refusing to display for me).

I'm going to finish that stuff up and get a functional base tune before worrying about the idle.

[iceminion]

Look guys, the FIAV is important.

Automotive makers try to save money everywhere, if this part was not important it would not be there.

My point is, the FIAV has nothing to do with bad idle.

[1QUICK4]

Originally Posted by iceminion

My point is, the FIAV has nothing to do with bad idle.

I understand your point, my point, my point was it doesn't warm the car up any faster than my right foot