Idle issue solved: 1988 Ford Bronco 4.9L (oem plastic T.B. gasket suck

ShadetreeSeattle

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Feb 21, 2017
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Had a problem with idle quality on a 1988 ford bronco with the 4.9L inline 6 (c6 auto trans) which kept stumpin me. it would when cold stall out the first start attempt or two, give it a bit of gas and it would eventually idle ok after a minute. after warming, the computer seemed to have trouble controlling idle. sometimes when put into park it would stall, or idle would hunt until it stalled. other times it would catch itself. acted similar to a vac leak, but was hard to find since the computer would cover it up by adjusting the IAC to full closed to compensate (vac gauge would show ok.) after weeding through things that use vacuum i was stumped. checked various engine sensors too as these can contribute to poor idle quality. i decided to pull off the throttle body since it looked gunked up pretty bad and low and behold the factory t.b. gasket had nearly sucked itself inside the motor, causing an un metered amount of intake air to bypass the throttle body. Moral of the story, if your throttle body gasket has never been changed, go for it. it was a buck fifty at the o'really's here. the factory (plastic?) gasket was fubar'd. i assume this applies to anything that was EEC from this time period, but unsure of when they changed from paper to plastic gasket. the plastic is so thin that it did not get good compression around the top and bottom causing it to slip inside the intake plenum/IAC casting reliefs in the T.b. Cheers guys and gals.

 

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