monkez

First, the brown-nosing: I really cannot begin to portray my appreciation for this forum. While I do not post here very often, the information that is provided here as well as the generosity of everyone with their time and knowledge is really humbling. Just reading the posts about everyone else's challenges and problems has really prevented a lot of head-ache on my end. It's truly appreciated.

The background: So I've been working on my intake refresh on and off for the last 8 months (i tried to take my time ) and have been trying to chase down a vacuum leak for the last few weeks. I won't go into detail on every test that was done, but suffice it to say that I found several mistakes that were made when putting everything back together. However, despite finding and correcting a couple of mistakes, the high idle remained and there was no obvious location for a leak. In frustration, I pulled everything apart with the intention of making sure everything holds vacuum as it's put back together.

During this process, I discovered that the o-ring that goes on the MAF (999-701-183-50) was never put on. In fact, I don't think my car ever had it in the first place, which is why it was missed in the refresh.

But I'm still dubious about this being "it". Just to make sure that this is the problem, i connected the MAF to the throttle body and sealed up every hole with rubber stoppers, covered the MAF with a 4" rubber plumbing seal and used a 3" pvc cap on the top where the air tubes connect and tested it to make sure that it holds vacuum.

Of course, it doesn't hold vacuum.

However, I realized that it may not be holding vacuum because of a screwhole to what I think is the idle adjustment screw.

The first pic shows the MAF/Throttle all buttoned up with the idle adjuster circled. The second pic show the screwhole that may be letting out vacuum.

My question: Should the maf/throttle hold vacuum when every hole is plugged up? Am i crazy or just monumentally ignorant? Is there something that I'm missing?



thanks!

davek9

Anything before the Throttle Body won't cause a high idle, just poor mixture.
It's the TB that in-conjunction to the ISV holds the Idle at rest and stable.

There is an adjustment on the TB itself, it is that brass looking Hex screw, counting the turns turn it in slowly to count how far out it is, as this can affect idle speed. That hole in the TB is a vacuum vent, not a screw hole.

What is the "high idle" RPM that you are seeing?

Dave

monkez

Idle was sitting at around 1100. Also, the car was *very* sluggish when accelerating.

thanks!

davek9

OK, I recently chased down a high idle after an intake refresh on my '85, what I did was block off all unneeded vacuum lines at the TB.

So you really only need the one that feeds the FPR and dampeners, all others can be capped off, this includes the ones feeding the Fuel tank vent, I never reinstalled it as I found the large black one vacuum mod was full of charcoal pellets sucked in from the canister in the fender well.

If you car is an Auto you will eventually need the Trans feed, HVAC from the Booster once you fix the idle leak.

If the ISV is not new that could be the cause and or the LH computer that controls it, a worn out ISV can also cause the computers driver circuits to fail ~ 1500 RPM idle however most common are leaks.

Dave K

hlee96

Dave, I know next to nothing to contribute to this thread, but I need to mention that that engine of yours is simply amazing!

monkez

Thanks for the feedback! In short, what your telling me is that I'm probably good to go. I say that because:

1. all items connected to 7 way splitter hold vacuum (including the trans).
2. All other vacuum lines from the TB holds vacuum as well.

I have a new vacuum check valve that I will put in, but I will need to fix the HVAC vacuum leaks as I'm sure those are toasted.

thanks again for the time and feedback!



In short, it sounds like

monkez

Oh and I agree with Hoi, that engine is beautiful...

davek9

Thanks guys for the complements, this was Mike Frye's old car from NJ, it sat for a bit outside and needed a bit of cleaning

I experimented w/ a different PC than I usually have done, the PC guy called it "near chrome" to me it looks more like a "Liquid Metal", I've been getting the water bridge's tumbled and like the results too.

I's a manual w/ PK S300 chips and pencil type 4 hole Injectors, X pipe, Hi-Flow CATs, next will be to re-do the CAT back.
My son had it out this weekend as I keep it up North where traffic signals are few and far between.

monkez

I really like the color of the PC. I actually thought that it was similar to mine, but yours is shinier and, if i'm being completely honest, much prettier. The color I had gone with was a "bare metal" look... so not as shiny (see below)

thanks again,

adam

Otto Mechanic

I don't know this would have much to do with your vacuum problem, but I had a scary moment when I discovered the MAF o-ring was missing. I was also searching for a vacuum leak during an intake refresh.

At first I thought the o-ring must have come off sometime during the refresh, then I found had dropped into the throttle. You might check to see if you have a stray o-ring in there? It's easy for them to slip off while you're replacing the MAF.

monkez

Actually, i discovered the o-ring was missing. Again, it wasn't on the MAF in the first place, which is how I missed putting it on. Hopefully, this is reason why the car was idling high and accelerating like s**t.

thanks!

Otto Mechanic

Just wanted to make sure you checked inside the throttle. I was more than a bit startled when I found that ring in the throttle body. Sort of like finding a dead mouse in the air box

Also, there's a tool you can build to test vacuum on the intake, I'm pretty sure it's on these pages somewhere but I can take pictures of mine if you still need it. It's basically a 4" to 3" reducing couple (rubber), a 3" PVC bushing, a PVC reducing bushing, a brass elbow with a shrader valve and a pressure gauge. You take off the air box, fit the gauge lashup over the MAF, pressurize the intake, and watch the gauge for leak down.

Like I say, I can take pictures. It's how I diagnosed my vacuum leak.

monkez

yup... did all that. If you look at the pics in the original post, you'll notice the 4" to 3" adapter on the MAF and plugs in *everything* looking to test vacuum on just the throttle body. I just had it plugged so I could test vacuum on just the TB. The original question was if this should hold vacuum since there is a vacuum vent (thanks to Davek9 for the term!) that may be letting out pressure. if it should be holding vacuum, then I need to keep checking.

thanks again!

davek9

Adam that is the same silver I'd go with for a stock look as the original didn't have any metal flake or gloss, just a plain metal look. I think it's the way to go for a stock look IMO.

As for that MAF "o" ring, it shouldn't effect your idle RPM speed, but will help keep dirt out and improve the air flow through the MAF for metering the mixture.

Thanks,

Dave

davek9

Your most welcome, IIRC that large Hole you pointed out directly corresponds to the Brass Hex Adjustment I pointed out, it is for Idle Mixture and is only used on the 85-86 MY's.

Did you turn that adjustment (slowly) to see how far in it turns?
Once you know, remove and clean it.

Dave