High Idle wont come down!!!

millhouse · Post by **millhouse** » Fri Jun 09, 2006 7:57 pm

I am running msns-e 029q with megatune v2.25 on a v3 main board.

The carâ€¦my 5.0l twin turbo mustang with mods as seen in my sig below.

Alright...I recently tried changing my r4 & r7 bias resistors to try to get more accurate megasquirt readings (see http://www.msefi.com/viewtopic.php?t=19611). While doing so...I ended up fouling out my plugs so today I swapped em out. Afterwards I tried lowering the req_fuel to scale the table down before starting. Well...I got it started, but it wouldnt idle down past ~ 2300 without making leaning the hell out of the ve table. Even then it wouldnt go much past 1500 rpm. Sooo...I swapped the original r4 & r7 resistors back in. Well...the afr now seems resonable...but once again I cannot get the damn thing to idle below 2300 rpm. I can back the throttle stop all the way out and it still wont come down. I'm attaching an old (running) datalog (good4)...as well as the new (high idle) datalog ("huh"). The msq is also there for your viewing pleasure.

One more thing worth mentioning is I screwed with the timing tables a bit with the msq. I tried reverting back to the old spark map but it didnt do squat.

feck · Post by **feck** » Fri Jun 09, 2006 11:44 pm

You have likely got a leak some where on the inlet manifold by the sound of it.
Hope that helps.

Cheers
Daniel

Bernard Fife · Post by **Bernard Fife** » Sat Jun 10, 2006 6:52 am

millhouse,

I agree with Daniel, this is almost certainly a vacuum leak. Listen carefully for a hissing sounds. Timing and fuel adjustments shouldn't be used to lower idle speed, this just makes the engine run badly.

If you can't find the vacuum leak externally (a hose popped off, for example, or a throttle body not tightened down) then look at things like the PCV valve, the or the intake manifold gaskets.

Lance.

millhouse · Post by **millhouse** » Sat Jun 10, 2006 8:12 am

Will do, thanks.

millhouse · Post by **millhouse** » Sat Jun 10, 2006 9:04 am

There are no vacuum leaks that I can tell.

Another unusual thing is If I unplug the vacuum line that goes to the megasqurt and inuce a vaccum leak, it idles down (runs pig rich). If I throw my finger on the line going to the megasquirt...it idles up a bit more. Remove the finger and back down it comes.

PSIG · Post by **PSIG** » Sat Jun 10, 2006 12:13 pm

millhouse wrote:...Another unusual thing is If I unplug the vacuum line that goes to the megasqurt and inuce a vaccum leak, it idles down (runs pig rich). ...

You are confusing MS. Although you are creating a vacuum leak by pulling the MAP sensor hose, you are also removing the reference signal to the MS. This is like stabbing it in the eye. It won't like that and will run poorly.

Air makes it run faster. Look for where the engine is getting more air. The engine is getting air from somewhere or it would die when you backed the idle screw all the way out. Maybe your IAC is stuck open or something. Good luck!

millhouse · Post by **millhouse** » Sat Jun 10, 2006 12:16 pm

PSIG wrote:
millhouse wrote:...Another unusual thing is If I unplug the vacuum line that goes to the megasqurt and inuce a vaccum leak, it idles down (runs pig rich). ...
You are confusing MS. Although you are creating a vacuum leak by pulling the MAP sensor hose, you are also removing the reference signal to the MS. This is like stabbing it in the eye. It won't like that and will run poorly.

Air makes it run faster. Look for where the engine is getting more air. The engine is getting air from somewhere or it would die when you backed the idle screw all the way out. Maybe your IAC is stuck open or something. Good luck!

Ahh...you beat me to it. I talked to a friend and he recommended unpluging the IAC valve....and BAM!!!! After bumping my setscrew back up it seems to idle fine. Now to find out weather it's the IAC itself or the main board.

maztah · Post by **maztah** » Sun Jun 11, 2006 5:49 pm

though you might have to return it again with IAC properly configured. It is helpful to start the engine faster and warm it up without being rich. Same goes with your A/C, the idle up when the aircon is on might be depedent on the IAC

millhouse · Post by **millhouse** » Mon Jun 12, 2006 3:11 am

maztah wrote:though you might have to return it again with IAC properly configured. It is helpful to start the engine faster and warm it up without being rich. Same goes with your A/C, the idle up when the aircon is on might be depedent on the IAC

That's the odd thing, I had it running with the IAC configured. After I swapped out the r4 & r7 is when the idle jumped up. I cleaned as much resin off the board as I could...and saw no problems on the board. Until I can figure out the problem...the IAC will remain unplugged.

I'm still open for suggestions on what to look for.

renns · Post by **renns** » Mon Jun 12, 2006 3:27 am

Think back carb idle mixture tuning. Typically you tune for highest vacuum(lowest map)/highest rpm, then reset idle speed, and repeat. Tuning MS is basically the same in the idle region. Once idle fuel is tuned properly, and idle speed is set correctly, there is no way MS can cause a higher idle speed unless it's opening a fast idle valve. Your engine must be getting a bunch of extra air from somewhere to idle above 2k. Vacuum leaks (as already mentioned, or a disconnected but leaking IAC valve might be to blame.

Roger