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Discussion Starter · #1 ·
I just installed a 75mm throttle body and SR aluminum upper plenum on my 2000 GT. Engine itself is stock to my knowledge with an x-pipe and Flowmaster style exhaust. The only other add-on is an SR cold air intake. My problem is that now my throttle will stick slightly open and idle high if I just step on the gas a little like when taking off slowly. It is a manual transmission by the way. I have the return spring attached as its supposed to be. When it sticks like this I just have to hit the throttle quickly and it will back down. While messing with it I thought the TP sensor was causing it to be jammed or the throttle plate shaft was sticking or binding. But when I was messing with the throttle when the engine was turned off the throttle would consistently close and go back to the stop and it felt like there was plenty of tension on the return spring pulling the throttle back. So why is this happening when the engine is running? Is there too much air rushing thru the throttle plate keeping it from shutting? How do I remedy this? I hate to put a stiffer spring for the return because all that will do is make the gas pedal harder to push and I really dont want that. Anybody else experience this? Any ideas on how to stop it?
 

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Dark Horse
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190 Posts
Your throttle is vacuum locking. It's very common thing when installing aftermarket TBs. Carefully turn the throttle rest screw in (or out, whichever way opens the throttle) a quarter turn at a time until it stops doing it......Just keep track of the original position in case it turns out to be some other problem.
 

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US Air Force (retired)
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+1 Classic signs of a vacuum lock. From the driver's side fender turn the TB stop screw clockwise 1/16 turn (I believe in small adjustments) until it stops sticking. You may also have a problem with the motor surging or stalling when slowing and turning. That would be because there isn't enough by-pass air going around the butterfly valve in the TB. Open it up a little (turn the stop screw clockwise) until it idles smoothly slowing and stopping. It you actually change the idle of the car then you have gone too far. Cliff Knight has a technical write up on this. It is under TB/Plenum then TB initial setup in the following link. PaladinMicro
 

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Discussion Starter · #5 ·
Thanks for the info. I will certainly look into it. I bought an assortment of throttle return springs made by Dorman in their Help line and took the one with the thickest material and the biggest (tho lesser amount) of coils on the spring and put it on in place of the factory return spring. I started the car up and it did seem to make it better. I cracked the throttle maybe an 1/8" from the stop screw as that is where it was staying stuck open and it closed each time altho not completely. It was much better and even tho it didnt close completely right away it did work closed within a few more seconds. I have not actually driven the car out on the road yet but it should be better as it was doing it right after I installed the TB right in my driveway without test driving it. Once I take the car for a real drive I will see how it acts and go from there. I appreciate the info and now I know what to do next. Thanks again folks.
 
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