High idle after throttle shaft seal replacement

[knochgoon24]

I just replaced the throttle shaft seals, now I can't get my idle below 1400 RPM, even with the BISS screwed all the way in. Backing the BISS out makes it idle surge. I'm pretty sure the TPS is correctly adjusted, since the idle position switch shows closed when I'm off the throttle and switches open as soon as I press the gas. I'm now pulling 20 inHg which is better than my old 18inHg at idle before the replacement. I figure this is due to the new seals, those old ones were leaking horribly. If I'm pulling more vacuum, how do I have a higher idle?

As soon as I put the car out of park/netural (auto), the RPM drop to 750 and sit rock solid, where it's supposed to be.

I logged what is happening on Evoscan. This is just very lightly moving the throttle.

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As soon as I let off the throttle, the RPM drop to 750 then climb right back up to 1500. If you need better resolution, tell me and I'll do another log just logging those 3, or anything else for that matter.

I would do a boost leak test, but I'm up at college. I checked all the intercooler clamps and they're tight. All vacuum hoses are also good.

 

[habitatguy187]

Might want to take off the TB and make sure the throttle plate is all the way closed when no tension is on the spring.

 

[LKWTSI]

Just did a TB shaft seal replacement on my 1G. I know, I know it's a 1G and yours is 2G, but the end result is the same. Unless you can do a valid boost leak test, you can't assume any of your hoses are tight and sealed. I did and couldn't figure out my leaks until I bubble tested them under pressure and low and behold 2 joints were leaking, even though, I thought I'd tightened them good and plenty. Turns out the clamp wasn't sitting on the lip right and tightening it actually caused the leak to get worse. POINT is do a boost leak test and make sure you have absolutely NO leaks, first.

Second, highly unlikely, but, almost made the mistake myself. With the TB elbow off look and make sure your butterfly plate is closing properly. If the plate is backwards it'll never seat properly on the TB surface and you'll get all sorts of problems.

 

[slowstang]

I'm pretty sure the TPS is correctly adjusted, since the idle position switch shows closed when I'm off the throttle and switches open as soon as I press the gas.

The tps is separate from the idle position switch. The tps is the black adjustable sensor on the front (in respect to the car) of the throttle body. The idle position switch is on the back side of the throttle body where the tension spring is and throttle cable hook up. Just because the idle switch say it's closed doesn't mean your TPS is adjusted correctly. Even if it is out of adjustment, however, it's not causing your problem. I agree with the previous poster... too much air is getting by. Hopefully you checked the blade to make sure it closes all the way when you put it back in. If you don't put it in exactly the way it came out it won't close all the way. Also if your throttle cable is too tight it would hold it open slightly.

If your idle switch is adjusted too much it could report the throttle being closed even if either of the above causes it to stay open a little.

 

[knochgoon24]

When I reassembled it, I made sure the plate sealed nicely. I forgot to mark it, but the plate was worn slightly angled. I didn't notice this at first, and when I put the plate in, I could see light around the plate when I held the TB up to the light. When I flipped it around so the beveled edge could "seal" there was almost no light.

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It kinda looked like the the left picture, but I exaggerated it to show my point. It was a very slightly worn angle, but it was noticeable upon closer examination. That way, when it seals in the throttle body, there's more surface in contact with the TB to seal.

I don't see how I can have a vacuum leak when my vacuum is now higher than it was before.

Maybe I need to try and readjust my TPS again... yay! That bottom bolt is a PITA.