this question is for the ones in the know on 4.6

i'll admit it, i don't keep up with the new technologies like i use to.
here's the symptoms - lincoln towncar 92, runs great going down highway, accelerating, all speeds above idle. gas mileage is 20 + which is about
normal.
sometimes at idle, and it will be idling beautifully, will all of a sudden break into a rough running lope, like it's cammed out. doesn't die.
picked up a new symptom. on occasion, will have pre-knock on at least one cylinder. so here you are, sitting at stop light, engine idling, with ping, ping, ping like you get when you turn off engine only it is running. give it some gas, it goes away.
i guess the joker in the deck is that it comes and goes. other times, the car runs fine and idles fine. i hate the intermittents. any idea as to what module is opening up or closing?
~ curtis
knowledge is power - growing old is mandatory - growing wise is optional
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Don't know for sure, but how about: plugged injectors? carbon build up in the combustion chambers? knock sensor? Kinda sounds like it may be starving for gas at idle speed which might be an idle speed sensor/throttle position sensor. Good luck and let us know the results. el lobo

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Is the check engine light coming on?
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Make sure that the rubber T fitting for the PCV system is not defective and leaking causing a vacuum leak. Common on that vintage. Stan K.
c palmer wrote:

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IAC valve, most likely. Remove it, clean it & replace it. Or, just buy a new valve.
c palmer wrote:

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hi folks - i'll try to add answers to the questions.
- check engine does come on after a couple of minutes. put it on the x-ray code reader and it came back with one code and it was for the EGR circuit, which is common for the 4.6's
- the "T" connector has been replaced. i'm familiar with how the engine runs with a bad hose connection and i agree with you that it will give you nightmares because of it's location. the clue about the mixture is that it will run perfect about 1/2 the time and sometimes it will just happen in the middle of the light cycle. it will just start running rough, like if you had a automatic choke circuit drop out.
- haven't done the IAC valve yet. like i said, i'm from the old school. can you give the basic idea of how it functions, location and maintenance of it. thanks.
~ curtis
knowledge is power - growing old is mandatory - growing wise is optional
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bad injector
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