Drove the car to work today and it's running very well. When I got home I wanted to check a couple things. Don't know why I did it, but the last thing was to spray some carb cleaner around to check for vacuum leaks. When I sprayed some under the plenum, she almost stalled out. Sumbitch! I thought I'd found all the vacuum leaks.

Question is, what's under the plenum that might allow it to suck air? Could there be a crack?

Great, gives me another excuse to wrench on the car. Also should allow me to lean it out a bit more at the AFM. It's L-jet, btw.

Any ideas?

Absotootly! It's just a metal box and they do rot out. Pull it and check. Easy, peasy.

Aliens

I can reassure you there are no Aliens under there. Don't worry.

Don't believe him, he was assimilated long ago

This is *exactly* what an alien would say.

Yup, seen plenty of rusted out plenums.

Thanks gents, that'll give me plenum to do this Saturday; I'll watch for both aliens and rust...

Looks fine. I don't know what was making it almost want to stall with carb cleaner but I'll go through everything again

At least I can clean up the compartment a bit.

Click to view attachment

How did you check it?

Run some green locktite across the welded seam. The green stuff is penetration grade and will seal any minor leaks in the weld.

water or air test it.

Thanks guys. Mike, I thought about using RTV or some such but the green Loctite sounds like a great tip.

Check the gasket between the plenum and throttle body?

Yes I had and it was bad, replaced it a year or so ago. It was when I sprayed the carb cleaner under the plenum that it would almost stall.

Make sure you have your accelerator pedal stop intact and adjusted to stop the cable from over torquing the plenum.

I went through 2 plenums the hard way on my /4 AX car before figuring this out.

Rob, had your's split at the seam underneath?

Double post

Check the trough-tubes on the plenum. Almost all cracks i have seen where around those tubes and they can be somewhat hard to spot.

A pressure or water test will show ...


EDIT: Oh, wait, this isn't a 2.0L? Nevermind then ...

Like Andy said. The plenum gets torqued by the throttle cable extended farther than the mount can go. The whole plenum contorts and lets in air. More structurally than the seams.

Andy, it's a 2056 with Ljet. Should that matter?
Trough tubes, are you referring to the runner connections?

Rob, I'm pretty sure the cable isn't yanking on the plenum, but I'll check after reassembly.

Thanks gentlemen

That's why i said "Oh, wait, this isn't a 2.0L? Nevermind then" ...

The 2.0L D-Jet plenum has hollow tubes that go through the plenum.
The 1.8L L-Jet plenum (which is what you have) does not.

And no, that has nothing to do with the intake runners.

Ahh, ok.

Danke

Sorry. I've only owned 2.0s and burned 2 plenums in succession Axing.

See, it's aliens.

Uh, Rich, I'm starting to think you're right...

It won't leak when you put it back together, therefore......aliens.

Ok, so, I put everything back together, started her up and tried the carb cleaner routine. Sprayed it under the plenum, and after a few seconds, the idle dropped and it wanted to stall.

Damn! No difference. No aliens either. So wtf?

Then, it dawned on me, after getting a whiff of the cleaner...

What was happening is the cleaner was getting heated, and then sucked into the snorkel. I verified it by adding a length of tube so it could suck fresh air from outside the engine compartment...

So I'm real good at removing and replacing the plenum now. Gonna add it to my skill set list

Car was running so well. Lesson learned, don't fix what ain't broke