Hanging idle, what to look at
Thread Starter
11 Second Club
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From: Northwest AR
Hanging idle, what to look at A member here helped me out with some tweaks on my tune until I can afford to get a dyno tune or get a wideband and learn to use it.
With this tune the idle likes to hang if I'm in park and rev it or if I shift into gear it jumps up then starts to fall but hangs high. Commanded idle is set at 750rpm and it hangs at 1200-1800 rpms for 30 seconds or sometimes longer before it starts to fall...but never falls back to 750, it will stop at about 850-900.
It's just irritating me honestly. I know 100% the throttle blade is not the cause.
With this tune the idle likes to hang if I'm in park and rev it or if I shift into gear it jumps up then starts to fall but hangs high. Commanded idle is set at 750rpm and it hangs at 1200-1800 rpms for 30 seconds or sometimes longer before it starts to fall...but never falls back to 750, it will stop at about 850-900.
It's just irritating me honestly. I know 100% the throttle blade is not the cause.
Have a look at what the IAC counts are doing.
If it crawls all the way to 0 and you're still too
high a RPM, that means there's an uncontrolled
air path to the intake. Vacuum leak, PCV, too
much drilling or blade off the seat, manifold
gasket leaks, etc. IF IAC is not falling to 0, you
may be hung up by some of the adaptive idle
limit values; there are min and max air g/sec
values that are "stops" for the RPM loop, and
if your base is too far off then limited trim has
limited effect.
If it crawls all the way to 0 and you're still too
high a RPM, that means there's an uncontrolled
air path to the intake. Vacuum leak, PCV, too
much drilling or blade off the seat, manifold
gasket leaks, etc. IF IAC is not falling to 0, you
may be hung up by some of the adaptive idle
limit values; there are min and max air g/sec
values that are "stops" for the RPM loop, and
if your base is too far off then limited trim has
limited effect.
Thread Starter
11 Second Club
iTrader: (18)
Joined: Mar 2008
Posts: 8,358
Likes: 27
From: Northwest AR
IIRC last time I looked the IAC were going to 0
I'll check the screw for the throttle blade and check for vacuum leaks, thanks! Not sure why it would idle right in gear though...I guess the load on the engine would demand a bit more air and put it back in the area covered by the IAC?
I'll check the screw for the throttle blade and check for vacuum leaks, thanks! Not sure why it would idle right in gear though...I guess the load on the engine would demand a bit more air and put it back in the area covered by the IAC?
