Throttle plate gap question

[spacecad3t]

I picked up a manifold and throttle body for my late model NA(87). It all looks very clean and the owner says the throttle body was rebuild not long ago. However, I noticed the throttle feels sticky and I see air gaps around the plate. I was hoping to swap these into my car, but Im not looking to add problems. Experts- are these gaps bad? Did someone install the plate wrong?

[Tom]

I'll check a few spares in the morning, but that doesn't look good to me. Any signed of the throttle plate screws being removed/replaced?

[rheidtman]

I would agree w/Tom... the lateral gaps appear to be off. Also, do be careful when trying to loosen the screws as they may have locktite on them... and if you loosen, you will need to replace this adhesive to ensure they don't back out while in operation.

[spacecad3t]

Any signed of the throttle plate screws being removed/replaced?

Yes, so this all tracks. Thanks Tom.

[Evan]

Yes, those gaps are a problem. A throttle plate should seal completely when closed. The sticky feeling and visible gaps mean it's either installed incorrectly or the bore is warped. Don't swap it in like this; it will cause a high, unstable idle. You need to fix this one or find another.

[spacecad3t]

Yes, those gaps are a problem. A throttle plate should seal completely when closed. The sticky feeling and visible gaps mean it's either installed incorrectly or the bore is warped. Don't swap it in like this; it will cause a high, unstable idle. You need to fix this one or find another.

Appreciate the confirmation.

[spacecad3t]

I spent some time trying to get the plate to seal against the bore better, this is the best I could get...

I have something causing a hot-high idle of 1100rpm. After much troubleshoot and smoke testing, I can only suspect that it is my throttle shaft or plate...

Question is- am I chasing the wrong thing? If I don't see smoke from my throttle body, should I not disturb it?

[Tom]

I pulled out a known-good throttle body and checked it. I ran this one on my car for years with no issues. On casual inspection, the throttle plate seals tight to the bore. However, I was surprised to see a gap when held up to the light. As a point of reference, it's a very thin gap -- a slip of binder paper slid in but was very tight and would get stuck after a few mm's.

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[johnb]

I am pretty sure the human eye can see light through a gap 0.001" so it's hard to judge things that way. Also the plate has some thickness to it right? So if it sealed perfectly then it could not open.

[Tom]

I am pretty sure the human eye can see light through a gap 0.001" so it's hard to judge things that way. Also the plate has some thickness to it right? So if it sealed perfectly then it could not open.

Google says my binder paper feeler gauge is .004" -- the gap varies around the circumference of the plate, from no apparent gap to just wide enough for the paper. I'll have to look at it more closely, but know some throttle plates are beveled so they can sue up closer to the bore and still open/close. As I think about it, as a production part I guess it's not surprising to see gaps in this range. I'm guessing the gap grows as the temp rises (aluminum bore vs brass(?) plate). I recently joked to my machine shop guy that I wanted a part machined to within .002" and he said, "sure, at what temperature".