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PLEASE HELP! I have a 2003 ford taurus ses. About a year ago it started running 3-4000 rpms when i put it in park. When I'm accelerating around 35-45 mph, theres a loud rattling under the hood and when I let off the gas the car briefly surges. Now it accelerates by itself and still wants to go when I'm at a stop. I've had spark plugs and wires replaced, gasket heads, pcv valve, MAF sensor, iac valve, egr valve, throttle position sensor all replaced. Throttle body and intake totally cleaned. Mechanic did a smoke test and found no vacuum leaks. Also had throttle cable checked, perfectly intact. No one can figure this out. Please help. Also sometimes if I adjust the pedals while going down the road the rpms increase.
 

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Motorcraft IAC or POS aftermarket part? The ONLY IACs that work on these cars is the Motorcraft unit.

Was the PCV valve a Motorcraft unit? Again aftermarket PCV valves are junk and can cause your issues.

What engine do you have? Vulcan or Duratec? IACs are different between the 2 engines, but will physically fit either engine so be 100% sure the correct Motorcraft IAC was installed.

What are the long term fuel trims on each bank? (Check with a scan tool that shows live data) High positive trims at idle that drop under load are indicative of a vacuum leak.

MAF issues are virtually unheard of on either engine. MAF can be checked by looking at measured air flow under various conditions with a scan tool to determine its health.
 

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Discussion Starter #3
The engine is a duratec. The IAC was not motor craft. I'm not sure about the PCV. That would make sense because the issue started right after PCV was replaced
 

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Must have MC PCV. Been there, done that, aftermarket is high flow and high rpm. In addition you will need the new hose/elbow as in the pic. Original often leaks.
Best of luck.
-chart-
 

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