Howdy All
A couple months ago I bought my '96 FS Bronco with the 5.0. Since then I have had it in the shop and as time allows I'm checking things out to make sure that it will be a reliable Daily Driver. When the EGR valve tested bad I replaced it so then I tested the IAC, which also tested bad so I ordered the replacement. Tonight I pulled the old IAC off to find that the PO, or his mechanic, had cut a piece of plastic to match the outline and bolt patter of the IAC gasket but the air flow holes have been mostly plugged. The gasket opening is in the order of 9/16", the modified plastic part has a hole less than 1/4".
I'm wondering if this is an after market mod to control air flow through the IAC for some reason.
Anybody have any ideas or suggestions?
Thanks in advance.

 

I don't understand the benefit of limiting air flow for idle, unless maybe the engine idled high from another problem, and that was the "fix" to reduce RPM? Other than something random and backwards like that, there shouldn't be a rigged piece of plastic on there.

 

Agreed, to be polite, this is a Home Brew Bugger.
I asked one of the mechanics that I work with that has far more Ford experience than I do. His suggestion was that the PO or his mechanic ran into an EGR system that was fluctuating the flow into the intake. That fluctuation might have cause surging at idle or slow down so instead of fixing the EGR they Buggered the IAC.
Anyway, the '96 now has a new EGR and IAC so when I get it on the road we'll see what happens.
Next target is to finish the fluids and then the exhaust.

 

If the IAC solenoid was failing, the "restrictor" would have kept the idle air flow "more-or-less" regulated. When a a solenoid begins to fail, the coil cannot hold the valve in position due to the weakened state of the coil that drives the bolt in the valve or a leaking valve seal. Add the constant vibration and impact shock of any component mounted to a running engine in a moving vehicle and the likelihood that a weakened solenoid will fluctuate grows exponentially.

Restrictor plates work in NASCAR to standardize the air flow into the engine at the throttle (i.e. every car/engine has the exact same size throttle bore even at WOT). It would work at the IAC in the same way. The only difference is that the IAC only handles idle air flow. If the IAC won't hold at the proper flow rate because of a dying solenoid or a leaking valve body, a restrictor plate in the IAC valve body would actually be rather effective with the critical exception being that a properly functioning IAC has the ability to vary idle air flow making the efficiency of fuel-air mixing far more accurate and effective than a single bore/size restriction. Since the IAC is only necessary at idle, the restrictor plate would be a cheap and relatively effective temporary fix to a failed/failing IAC.

 

That is a great explanation, I appreciate it.