1999 Ford F-150 Location of the IAC unit on the intake manif

4.2L, 4.6L or 5.4L engine?

It is located on the left side of the intake manifold, pictured below..

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Example pic of intake manifold is below..

A few different things to do to clean out your intake manifold are below:

Simply use some air intake system cleaner. Then use a product called BG Fuel Injection System Cleaner. Get a can tap (like an A/C freon can tap) and open a non-pressurized can of Fuel Injection System Cleaner. Take the end of the hose (attached to the can tap) and attach it to the vac. port that's right after the throttle body. The hose has a .025 orifice and lets the Fuel Injection System Cleaner vaporize into your manifold over the course of about 10 mins (12 oz. can).

After this try some fuel additive.

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