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Discussion Starter #1
Changed my throttle body & harness to match to try & fix my rough idle problem I've been having. It threw a low voltage tps code once so i figured the tps was bad. I had one of those old tps before Ford did the revised version.
Anyway i installed the new one but i notice that the idle is still rough when i put the car in drive but it smooths out when i turn the AC on, turn the AC off & it idles rough again.
Anyone know what would cause this?
 

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Sounds like you must be the only guy on FF that has an IAC valve that is actually working right. What RPM is the car idling at w/o the AC on ? and with the AC on ?. I`ll bet it gets higher with the AC on (as it should). Any time there is a load at idle put on the engine, IE, AC or turning the wheels while stopped. The Idle Air Circuit valve will respond by increasing the engine speed. Could be as simple as getting the normal engine rpm raised.
 

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Discussion Starter #3
It idles at around 1000 rpm without AC, with AC it goes up to 1100 then drops to 900 and idles smoother at that speed. Not as smooth as I'd like but noticeably smoother.
 

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It idles at around 1000 rpm without AC, with AC it goes up to 1100 then drops to 900 and idles smoother at that speed. Not as smooth as I'd like but noticeably smoother.
Is that in gear or neutral ? 900 rpm is good idle speed. You can try this. Ultimately , the computer controls the idle. Disconnect the IAC. Start the car, set the stop screw on the t/b to 750 rpm in neutral. Plug the IAC back in. Then let the car idle for 5-7 minutes. This should reset the idle speed. If it still wants to go higher , then you will need to have the computer reset to the idle speed you desire.
 

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Discussion Starter #5
Yeah, I had the gear in neutral monitoring the idle speed. I'll give it a try & let you know. My biggest problem though is really the roughness of the idle, too much vibration with the engine running, someone said i may have a vacuum leak somewhere.
 

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Most common is the PCV , hose. As it turns towards the intake manifold. It will either get soft and suck itself shut at idle. Or it will fall apart.
 
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