CalBoy101

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?

cliffyk

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...

Grey-03-GT

In plain english...ok then after the mod I adjusted the" throttle body stop screw" to 0.010" with a Allen wrench in those threads JJ Glo... and it runs and idles just right.

Green03GT

Just wanted to say this is a great forum, we new guys need this. I have the same problem with 03gt. Thought maybe the iac was going bad. Think I give this a try seems simple.

cliffyk

A couple of points:

• 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...

Green03GT

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...

cliffyk

You will not completely lose the brakes, just the power assist.

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"...

Green03GT

Man great right up I've always wondered what in the world was going on. Makes total since, good job cliffyk

kilr95ss

Thumbs up for the 1/2" cap in the IAC tube, worked like a charm.

dlpich63

Ebay sells a IAC restrictor plate for 86-04 Ford 4.6 v8, I have a 98 gt that is molded and chipped and this fix works great