Throttle body air supplies


Lets start with both 8v intake man.'s, you can see TB base mount here and the small rusty water hole"H2O" and the other small hole is iAC air. (add bleed in 1991) at this base mount. There must be no air leaks anywhere here.

My Throttle body slide show. 8v TBI first The Dash Pot retracts at 30seconds max, after start , the TV is closed 99.9% , the IAC closes at 158F and the Bleed screw + ISC are the only air sources HOT. This old throttle body love to fail in many ways, Air leaks, all cause idle speed too high.

the mid gasket love to crack suck in and then leak fresh air and idle speeds scream, out of control, the base gasket must be formed correctly if not and you fail to block the holes that must be blocked, bam, sucks illegal air.

how the gasket fits, (it likes to crack and suck in here) the IAC suction port can be seen here, one can block this with clay to find a bad IAC stuck open. a trick that is super easy and very fast way to find any bad ISC on 8v engine, the 16v this can be done too but, port is wide slot.

starting in 1991 they added the bleed air screw. for idle duty cycle setting.

my 100% clean TB. the allen wrench is never used , unless the ISC set starts to leak too much. set it so the ISC pistion seal just barely touches seat if you dont want to buy a new $200 ISC.

the 1991 bleed, never seen before this year.

see white paint, that means don't touch it. Factory set for ever. I found one car that someone fiddle the screw, so used a 0.0005" inch feeler gauge and set the fly plate to bore gap. to that ammount, note the 3 zeros to the right of the Decimal point. 1/2 thou. setting. This is so close that water will not pass by valve. and the only purpose is to keep the valve closed and not jam or wear the bore. The intent is zero air flow here. !!!


8V IAC air flow rules , factory SPEC.!

poster cut up both valve. the below, IAC is real good. the ISC is open cold if not its bad, if it stick open above 150F that too, is a bad IAC. photo by Luis Carlos, and comments by me.

here my cut up, done long ago to the ISC (electric)

look careful here, see those gaps, i took those gaps carefully using number drill shanks. "very accurate" same with temps there, accurate.


the early 89/90 TBI has no hot water ISC, and no Bleed air screw.

this curved path must see vacuum from the plenum, one way or another. on both the M/T and A/T there are small hole below TB that MUST be blocked, if not, max pain. Do not GUESS at gasket,s buy a real set and WIN. The slot here with red arrows is ported vacuum it must have a slot or a hole on the right (bid red dot) or you will never get ported vacuum.

A/T-only PTC heater, only 89/90, not used starting in 1991 it heats up for better cold start vaporizaton of the fuel.

PTC agiain, A/T only, deleted in 1991.

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