99 explorer 4.0l(pushrod)idles at 1500 at start up then drops to 1100

all in the workshop manual which you are well advised to invest in

Sounds like a typical failure for an idle air control.

I'd recommend sticking with OEM, my experience with Chinese IACs is mixed at best.

Vacuum leak from brake booster. If you hear a sucking noise when you press the brake pedal replace it. Another way to check it is to place truck in gear set e-brake press brake pedal repeatedly and see if idle goes up and down. DO NOT PRESS GAS PEDAL DURING TEST.

FOLLOW LINK.http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?fromSearchPage=true&pageId=0996b43f80378c6a&partName=Throttle+Position+Sensor&partId=0996b43f80378c6a

Have you adjusted the pushrods properly? Pushrods generally need to be adjusted after installation.

Not sure how to do this on this model, although I own a 94 Ford Explorer with the V6 4.0 Liter motor.

Basically, when a gas engine doesn't run, you check 4 things, and narrow it down from there.

1. Gas (Is gas pressure good, is gas flow strong enough?)
2. Spark (are all spark plugs firing properly? Is spark strong enough)
3. Combustion at each cylinder (timing, pushrod adjustment)
4. Air Flow (MAF/MAP sensor working? Air Filter dirty?)

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Check your vacuum lines for leaks. Symptoms suggest vacuum leak.

It could. Be sure to clean the throttle body first. Open it wide open and take an old toothbrush and carb cleaner and make sure its clean. Usually when the IAC is bad, when you firsty start the truck the idle speed will "flare" to like 12-1500 rpm, then settle down to 7-800. If it doesnt do that, then it could be bad.

a common problem with ford 4.0! idle air control !aka iac motor! and throttle position sensor

if it only does this when its cold its normal, the car is just setting a higher idle to warm up the engine