88 Sub intake manifold coolant leak, the fun begins

Threadlock BLUE formula (medium strength) is what to use.

Doc

In this year, it's very important to use a pipe sealant on the middle 4 bolts. Their holes in the cylinder head are not "blind" and need to be sealed, otherwise you will get oil wicking up the bolts. It's also critical to put the intake manifold bolts back in the exact holes that they came out of, as the ones in the middle should be a slightly different length. If you mix them up, often you will have a bolt in the middle putting pressure on one or more of the pushrods and causing all sorts of nasty things to happen.

Ian

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-

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

I'm just wondering what the hell you're talking about. There is no idle set screw on throttle body injected engines. The throttle plates are supposed to be completely shut; the only air the gets into the intake during idle is via the IAC valve. So whatever you were toying with, it wasn't the idle set screw!

Regarding the gasket, they all look like that after 100k miles, just regular aging.

Doc

Yes there is an idle set screw on the 88 5.7 tbi. It is used to set the base idle when the IAC is fully closed. According to the factory manual the ECM is put into diagnostic mode by shorting the A and B terminals. Then the ignition is turned on and the IAC fully closes. Before starting the engine, the harness is disconnected from the IAC so it will stay shut. With the engine up to temp and in gear it is supposed to idel at 525rppm. This set screw is used to adjust that "base" idle speed.

The procedure is spelled out in Emmisions, section 4 in the back of the factory service manual. The screw is referred to as a "stop" screw. It's easily identified visually as a throttle stop screw on the TBI.

I returned it to it's original position when I found the plates were already fully closed. The embarassing part is I didn't see the pieces of gasket sticking out into the throat of the TBI until after I removed it.

-RC

R.Clarke spam snipped-for-privacy@BlocKmindspring.com RTP, NC, USA

Looking again at the base of the TB, I can see where the original intact gasket was placed. It looks to have been installed properly. I wrongly dissed the factory guys.

This is the first base gasket I have ever seen extrude into the throttle openings. I've pulled many a loose carb and a few throttle bodies and never seenclose to this kind of movement (over 1/2 cm).

-RC

R.Clarke spam snipped-for-privacy@BlocKmindspring.com RTP, NC, USA

That's because these base gaskets are quite thin, compared to the older base gaskets that used to come on the Quadrajets. This happens all the time with these gaskets....and other areas around the engine where this type of gasket material is used.

Ian