It wasn't long ago I posted about this truck having a fast idle. I don't remember who, maybe Doc or Refinish King who said a vacuum leak was often the cause. I'm still acquanting myself with the finer points of fuel injection so that wasn't the first thing I thought of.
The first thing I decided to do was waste money. I replaced the IAC valve. I figured hey, it's only $30. Needless to say that didn't do a thing for the fast idle.
Next I tried reading the manual. I put it in diagnostic mode, unplugged the IAC after it had shut, then fired up the motor. Still a fast idle(800+rpm in gear). I popped out the anti tamper plug and tried adjusting the base idle with the idle screw. Backing it out didn't do anything. The plates were already full shut.
At that point I figured I really did have a vacuum leak and decided it was time to take off the manifold. It already had a coolant leak so it made sense it would leak vacuum too.
Here's what I found when I took off the throttle body-
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Caution, these are big pictures, 700KB each.
Best I can tell the gasket was screwed up at the factory. That's the only way I can explain the idle set screw being backed all the way out and plugged. The bolts on the throttle body were snug. Everything else on this truck is original, why would the throttle body base gasket be different? The original owner didn't even change the distributor cap in 90k miles. Otoh I find it hard to imagine the factory could mess up a gasket this bad.
Anyone want to hazard a guess how much I'll need to turn in the idle screw after I replace this gasket?
-RC
R.Clarke spam snipped-for-privacy@BlocKmindspring.com RTP, NC, USA