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First off, I have a 1995 Mercury Cougar 3.8L. It has been fully tuned up, plugs, wires, air and fuel filter, cap, rotor.
When I start it from cold the rpm shoots up to about 3000 for about 5 sec. Then slowly goes back down to idle, 650 to 700 then starts to miss. Accelerates and cruises down the road just fine, no miss. Only at an idle, warm or cold.
Now if I'm driving down the road, rpm's at about 2700 and I let off the gas it keeps going, putting it together in neutral and the rpm's spike to about 5000. I replaced the air idle control valve hoping that's it but there was no change. I'm afraid if it keeps starting like that I'm going to mess up my valves. I can already hear them click when starting but that goes away when the idle drops.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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What happens if you leave the IAC unplugged? Is the throttle butterfly closed completely?
 

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Discussion Starter #3
Not completely. There's probly a .55 gap or so. And if I unpluge it the car will idle rough and then die.
 

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Discussion Starter #4
So I checked agen yesterday and it is completely shut nut I noticed if I cover half of the air idle control valve while its idling it gets amazingly better. And I don't have any vacuum leaks as far as I know. Dose any one know what the apsi reading is that I should get if I hook a vaccum guage up to it.
 

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you should pull over 15 inches of vac no problem

make sure the iac valve is not mounted backwards

a .55 gap is over a half inch, did you mean .055?

it definitely sounds like an air leak, check the egr and purge hoses too, if the solenoid is actuating and they are opened to air it will cause a hellacious air leak
 

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Discussion Starter #6
Yes .055, lol is there a way to bypass the perge system without making the computer go crazy, and I'm also thinking of bypassing the egr, I'm up I'm mn so I don't really need all the emmisions crap.
 
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