TOPIC: '97 Chevy Suburban 5.7L Vortec TB Grooved w/ IAC Mod

This TB was Grooved for Jon H. in North Carolina. Jon has been following the Groove for some time. He's upgraded his ignition, exhaust, and other things in search of better efficiency. He said that the Groove will top off his efforts on his '97 Suburban. We will await his results and comments to come!

This TB is cable drive, w/ an integral Idle Air Control valve (IAC). The upper bore has a big rectangular port to feed air to the IAC valve. I learned from Ron way back in 2012 to restrict IAC airflow since sometimes ECM will hold the valve open even when the throttle is open too. This acts as a vacuum leak, in direct conflict with what the Groove does.

The idea is to restrict, but not eliminate the flow thru an IAC. An engine can't run w/o idle airflow! This TB is typical of many GM V6 and V8 engines of the 90's. Throttle is fully closed at idle- if your foot's off the pedal, the plate is closed. FYI- this IAC valve is a reversible DC motor that extends and retracts a pintle, sort of a hard rubber "nose" that seats on a round bore. Not visible here, as this TB was bare w/o it. It's a judgement for how big the final opening will be, it still must allow enough air to support both a fast and curb idle RPM.

Large bit Groove done on this one. Two places where the bit will break through. Inside the lower IAC channel, the throttle bore gets to half thickness.
Close to the return spring end of the shaft, is a small thin spot.

I learned to examine any TB before Grooving, checking throttle bore wall thickness. I look for likely thin spots that could break through. I like to JB those spots before Grooving, if I can.

I use a drill bit or similar to rough up the metal, to improve bonding of the JB Weld.





I inserted a hose wrapped in clear box tape into the IAC valve bore. This closes the upper and lower IAC channel , sealing the base of the upper channel. JB won't stick to the tape once cured, The hose acts as a mold for the epoxy, the tape is a mold release agent.


The rectangular channel is filled w/ JB Quick epoxy, cured and sanded to be close to the bore wall shape. This epoxy fill did come out a bit rough, but it will work OK. W/ Hose removed, the hole is drilled through the epoxy to intersect the lower IAC valve bore.



Large bit Groove broke thru in 2 places: the lower IAC channel, as expected, and around 3 cuts in from the left start end of the Groove. A tiny hole close to the throttle return spring. First one was pre-epoxied in the IAC channel in anticipation. Second tiny one was unexpected, epoxied over on the outside, then a quick re cut w/ large G-Man bit to clean up in the Groove. IF you epoxy over on the outside surface knowing/believing it can break through, and it does break thru- your Groove is fine, no extra work needed.




Like Ron's G-Man training says, folks- Check your Work w/ a bright flashlight after cutting your Groove! Even a small pinhole breakthru can spoil your work, causing a vacuum leak.

To finish this one up, I sandblasted it clean. Mr Jon will hopefully give us some feedback on this one, I fully expect success!!

Tracy G

Once again, Tracy, you have impressed me with the quality of your write-ups, documenting your work. Additionally, you remember and SHARE the proper techniques with (dare I say this about a real Gadgetman?) true precision?

First, the modification. Superb! I know the limitation to 5 attachments, but I am going to fix THAT in a short minute! Allowing 20 should be more than sufficient. Agreed?

Second is the reason I say this. it would have been EVEN BETTER!!! if you showed the IAC passage on the throttle body after your work and it is ready to install! :frown:

I wonder... If I were to schedule an in-person class for a week once a year, would you be interested in being the primary instructor?

Just thinkin'......

After all, if not for you Gadgetman Groove online would not be here today. Add to that the precision in your mind and how much a stickler for detail you are, not to mention truly honorable, makes you a wonderful instructor.

Whaddaya tink 'bout dat, big guy?

Thanks for the thumbs up, Ron!
I was attaching a 6th pic, but hit the limit, so raising the limit is useful. I took over 20 pics, so I will see about adding more.

Sure, I can teach a class. I promise to (try) not to be Class Clown!

I unknowingly took videos of this mod, thinkin' it was pics only...I never did apply to do overhead imagery analysis for the NSA....

good thing I was too young for that in October 1962...

Ok, I'll behave....!
I hope the pics and comments I made might help another Gadgetman or Gadgetgal

thats why I do it like this.

my Dremel is still hungry...!

Tracy G
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