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Discussion Starter · #1 ·
Hello,

I've been struggling with high idle issue since I cleaned my 2.0l cougar's throttle body. The car now always idles at 1100 rpm when at a stop, whether the engine is warm or cold. Something even stranger is when I press the clutch or put it in neutral while rolling, the engine jumps to 1500 rpm and will only drop back to 1100 rpm when I come to a complete stop. Also, the car now has little to no engine braking and almost accelerates by itself.

I already tried to replace the TB gasket, as well as the TPS sensor. Also, I don't hear any whistling sound that would suggest a vacuum leak. I read a clogged IAC valve could cause those symptoms, but it seems unlikely that it could have failed right after I cleaned the TB, since the car idled normally before the job.

Any idea of what could cause these symptoms?
 

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You're one the right track. Its either a vacuum leak or the idle air valve.
 

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Did you remove the IAC valve before you cleaned the throttle body? I made the mistake of leaving mine on when I cleaned my intake manifold on my 2.5L V6 and that screwed up the IAC such that it had the same symptoms you are describing. I ended up having to buy a new IAC.
 

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There should be a way to check the IAC valve to see if it is working. I recall that there were 3 wires going to it: positive, negative, and a signal wire. If you put a multimeter on it and move the throttle, the signal should change dynamically. If not, it's dead.
 

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81721
 

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Discussion Starter · #8 ·
Well guys, thank you very much for your help. I'll go have a look at all your documents.

Today, I tried unplugging the IAC connector to see how the engine ran without it. With the IAC unplugged, idle dropped to around 800rpm as it should normally. I have read elsewhere that unplugging the IAC should lead the engine to run around 4-500 rpm, suggesting that a higher idle without this valve would be causer by a vacuum leak. What are your thoughts about that?
 

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Yes, sounds like a vacuum leak. Could still be the IACV leaking by.
Did you disturb the throttle stop screw when you cleaned the throttle?
 

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Discussion Starter · #10 ·
Well, thank you all for your help. I finally managed to solve my crappy idle problem simply by replacing the TB which was definitely causing the issue. Seems like cleaning those plastic TBs can easily damage them... Which is good to know
 
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