How To: IAC Rev Mod (Fixing the hanging RPMs)
#91
Well I just gave this a shot, got the 1/2" cap, put a 9/32" hole in it. It fits in the center section of the IAC inlet hose perfectly.
I disconnected the battery for 10 minutes then started the car. It started totally normally, let it warm up for I think at least 15 minutes and during that time the idle dropped down as expected.
But then problems. When you goose the throttle it still hangs up, probably even more. But then it never settles down to a normal idle, it hunts between 1000 and 1200 or so.
While this is going on you hear a weird buzzing noise. I thought it must be the IAC valve so I put my hand on it but didn't feel anything so I can't say for sure that's where the noise is coming from.
I took the cap out, connected my data logger and restarted and then the car was back to normal.
At idle the IAC parameter sits constant at 33%. If you goose it hard it rises up to 50%, stays there for a couple seconds holding the rpm's up then it drops down to 33% and the car comes back to idle. The car is running great so it doesn't have any vacuum leaks or other problems.
Any idea why the trick isn't working on my car?
I disconnected the battery for 10 minutes then started the car. It started totally normally, let it warm up for I think at least 15 minutes and during that time the idle dropped down as expected.
But then problems. When you goose the throttle it still hangs up, probably even more. But then it never settles down to a normal idle, it hunts between 1000 and 1200 or so.
While this is going on you hear a weird buzzing noise. I thought it must be the IAC valve so I put my hand on it but didn't feel anything so I can't say for sure that's where the noise is coming from.
I took the cap out, connected my data logger and restarted and then the car was back to normal.
At idle the IAC parameter sits constant at 33%. If you goose it hard it rises up to 50%, stays there for a couple seconds holding the rpm's up then it drops down to 33% and the car comes back to idle. The car is running great so it doesn't have any vacuum leaks or other problems.
Any idea why the trick isn't working on my car?
#92
You need to drive the car normally/somewhat agressively for 25 to 50 miles; "goosing it" from idle accomplishes nothing. The PCM needs to relearn the idle air and virtual "dashpot" trims (and other adaptively learned values) after resetting the KAM...
Last edited by cliffyk; 10-07-2013 at 07:21 PM.
#95
- It is normal for the engine speed to hold high an annoying bit between shifts--this is what the IAC mod is intended to "fix";
- It is also normal for the idle to hold high while rolling to a stop. This is done to ensure sufficient pressure in the hydro-boost braking system for safe braking--making the IAC mod too restrictive can cause the engine to stall at closed throttle, causing sudden loss of power-assisted braking; this is bad;
The IAC can be fully tested as described here...
#96
Ok well this seems normal with my car it seems to run great. I've notice some humming coming from my IAC every since I cleaned it out. I will test it as described tho. I remember when I first bought the car new from ford, it seemed when I engage the clutch my rpm's would be around 1000 now its more like 1300-1500 then come back down to regular around 8-850 or so. Your right losing my brakes would be bad...
#97
Ok well this seems normal with my car it seems to run great. I've notice some humming coming from my IAC every since I cleaned it out. I will test it as described tho. I remember when I first bought the car new from ford, it seemed when I engage the clutch my rpm's would be around 1000 now its more like 1300-1500 then come back down to regular around 8-850 or so. Your right losing my brakes would be bad...
The IAC hums because centering vanes on the valve plunger are worn allowing it to vibrate in the housing--more about that here. In your case it is likely that cleaning it removed some carbon build up that was dampening its motion.
There is no repair for this, the IAC needs to be replaced--in fact Ford makes it clear in the shop manual that the IAC "cannot be cleaned"...
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zanemoseley
2005-2014 Mustangs
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09-06-2015 12:58 PM