Question about 2002 Mercury Mountaineer

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O2 mountaineer my 02 mountaineer at 500 to 1500 rpm air is going back to the air filter but anything above 1500 rpm it runs great

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  • h_hoing Feb 25, 2009

    it is a 4.6

  • h_hoing Feb 25, 2009

    thats not the problem still can not figure it out

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  • Mercury Master
  • 783 Answers

You didn't say whether your engine is a 4.0L v6 or a 4.6L v8 but if you have an excessive amount of air blowing back into air box and vehicle is running good otherwise you may have a stuck open PCV valve causing it to pull to much vapors from engine crankcase.
If it is a 4.6L it will be located in the valve cover itself.
If it is the 4.0L locate the hose coming off of the back of the upper intake and it will be at the end of this hose. This one you twist CC to remove.

Posted on Feb 25, 2009

  • Chuck Martin
    Chuck Martin Feb 25, 2009

    Well I am trying to make since of what you are telling me. See engine is nothing but a big air pump,it pulls air in and pushes air out. If you have air pushing back into the air box it has to be coming from some place like PCV system or you have a restriction in the exhaust. However the later should also show up during driving,car should struggle at the higher RPM's like you are running into a wall or a strong head wind.

    Have you tried unplugging the other breather line from the other valve cover that goes into the air breather hose between MAF and throttle body to see if this takes it away?

    You can check this vehicle for an exhaust restriction with a vacuum/pressure guage. Hook it into one of the hoses going from the DPFE sensor in the back of the engine that goes down to the exhaust. You should have 1 psi or less at idle and 3-4 psi at wide open throttle.

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Comment by the FixYa Moderator Staff:

We do not think that the fuel filter has anything to do with your issue. So, we would not recommend changing it.

We do not think that the TPS (throttle position sensor) is also not part of your problem.

However, we do agree that the IDLE AIR CONTROL valve could be your problem. If the valve does not pass a fixed amount of air into the engine, the car will not idle.

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