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Hello,

I've been having rough idling problems that I have been slowly fixing.

After cleaning the Mass air flow, replacing the PCV valve, cleaning the front oxygen sensor, I read about the collapsed PCV house, so I checked my in the back and lo and behold it was collapsed. I bought a new one from Ford and voila, no rough idle pretty much anymore, but there is still one minor problem.

When Im in parked and then after I rev the gas pedal up really high, it doesn't come back to normal idling but idles down really low, just to the point of stalling but then comes back to normal.

No check engine light is showing. What could be the problem? Other things I havent checked is the throttle position sensor and IAC?

THanks for the help!

Kevin
 

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I suggest going for some easy stuff first. Verify that the vehicle is in top running condition by going through this list.

1) spark plugs: check, clean, re-gap or replace if needed
2) spark plug wires: if lifetime warranty wires, replace for free, if not get some if needed. There are 2 tests for bad plug wires. The first is turning the AM radio to a frequency where there is no radio station. Turn up the volume and listen for pops in the sound of the engine as you rev or drive it. Second is to spray down the wires with a household cleaner like Fantastic, and start the engine at night. Look under the hood, and if you see sparks popping in time with a miss in the engine- replace the wires.
3) MAF: clean with spray cleaner.
4) Air filter: inspect or replace
5) Throttle body: clean with carb cleaner and a rag
6) Idle air control valve: remove, clean with carb cleaner and Q-tips so the shaft is clean, replace with gasket: $1
7) Reset A/F ratio: Remove the neg battery terminal for 10 mins. Replace the terminal, start the engine. Allow the engine to idle for 7 mins or so until the idle drops down to normal. Expect the idle to be high around 1k rpm, and will be fluctuating slightly. On a completely cold engine that has sat all night, this test might take longer. The actual test starts as soon as the engine is at a certain cylinder temp, and lasts for 5 mins. If you touch the accelerator during the test it will restart the test.

You should perform the last exercise after any time you make any modification or repair to the engine related to fuel or air except changing a fuel filter.
 

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Have you changed the fuel filter? On my ZXW, changing the fuel filter made a big difference in idle and engine vibration - at least it felt that way to me!
 

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Have you changed the fuel filter? On my ZXW, changing the fuel filter made a big difference in idle and engine vibration - at least it felt that way to me!
This fits right along with what "whynot..." said about going for easy stuff first. I would also suggest using some injector cleaner in combination with the above procedures.
 
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