IAC THERMO TESTING:                                                       
Idle AIR Control, this device is 100% thermal controlled.

This device, is open below 158F coolant temperatures, cause a real fast idle.
The colder the faster.
I did some simple reverse engineering below,  see the -10F?  and the cone gap.
The below is dismantled for easy viewing of the guts. See my slide show.

I think air flows from the right port to the center cone.(cold motor)
BELOW is the 16v version of the IAC/ISC.





This device provides extra air to the engine during cold start and cold start warm up, up to about 158F[spec] mine closes at 150 Degree's F. (data ;off 3 bodies)
Mine closes 8 degrees earlier than spec.  I'm sure that was Suzuki's intent.
Find at  which point it closes. ( slowly it does this)
It can clog, so clean it. (carb cleaner works)
You can test it only 3 ways.
way1:
Remove it, put it in a pan of ice water and notice it is open. by looking at the valve or blowing air thru air ports.
Then put it in 160Deg. F. water and notice it has closed up.
It is a thermo Air valve.
Those measurements in red above on my 8v were take on my car and using drill bits as feeler gages.
way 2:, is on car,  remove cover at 180f coolant temps (block) and see if the cone is closed fully, IT MUST!, (easy , huh?)

way 3: If not sure the way2 gap is closed after 158F, then pack the IAC port above with clay. I fill the whole cavity, don't be shy , pack it full.
See the Large circular pit with 3 , triad screw holes, pack that full. If Hot too fast idle speed, is cured, you have your reason (a bad IAC)

Note: I had a gasket kit handy before I started testing.  (you can make one easy with an Exacto Knife, and stock gasket paper.
In fact the cover makes stencil form.

Most stores sell this gasket kit. (beats $1000_any day)

Best source for these parts, are a wrecker ,as the factory parts are very expensive.  ($1000?, if sold at all)



The 16v IAC sucks air from there.


16v view 2:

ver.2



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