Suspected Vacuum Leak, Need ideas PLEASE HELP!

OK, so a lot has happened since I've last updated.. I replaced all ground straps with 4 Gauge Welding cable, I cleaned all grounds and put ox-guard on all cable lugs. I also added some grounds to. My idle is running at about 1400rpm and I have been doing some trouble shooting trying to rule out all possible sources of a vacuum leaks.. A few weeks ago I replaced the intake/exhaust manifold gasket and torqued all of the bolts to spec, so that eliminates the intake or exhaust manifold as a source for leaks. I also replaced the throttle body gasket with a new one. I checked the IAC by replacing it with a new one and saw no change in the idle. I went on to plug every single port on the intake manifold and started it to see the idle at 1300-1400rpm. One by one i replaced the tubes and started the engine and the only two that showed any increase in idle speed were the tube that goes to the rear of the valve cover I think its called the ccv tube but this only showed an increase of about 75-100 rpm and I have a new one to pick up at NAPA. The other increase i saw was only about a 50rpm increase and that was the tube that went to the break booster check valve. Other than that Blocking off all other places did nothing to lower the idle, actually now that I think about it I recently replaced the stainless steel tube that goes from the intake manifold to the exhaust pipe, I thought i got it tight enough but Ill check that tomorrow. Anyway that's where things stand. I have replaced and recalibrated the TPS.. The throttle body was removed and THOROUGHLY cleaned and replaced with the new seal. Does anyone know what the amount of space that should be between the throttle body and the blade on the butterfly valve in the TB. there is space all the way around the blade but I'm not sure exactly how much is suppose to be there, does anyone know the tolerance of this? The only other two lines are the one that goes from the front of the valve cover to the air intake and the other from the air intake to the cylinder shaped vacuum canister on the passenger side by the firewall.. Neither of these should matter I don't think. Anyone with Ideas Please help!

The first thing I thought of when you said you replaced the intake manifold gasket is: did he scrape off all of the old gasket. If there was much of any of that old gasket left then no matter how well you torque those bolts it may not seat properly. And I have seen where a cast aluminum intake after it was taken off warped for no reason other than it was cast aluminum. Did you have the problem before you replaced the intake manifold gasket?

The reason I removed the throttle body in the first place was to clean it so that I could make sure the IAC valve had a clean seat for the pintle.. I did have the high idle which is why i was investigating the IAC in the first place. Also it just kinda looked dirty and had some carbon buildup. Do you know the torque spec for the three TB star bolts? I can try to torque them down again? I tore the original gasket and when I reinstalled the TB originally I just used formagasket, someone said that wasnt such a bright idea so I scraped all that off and used a red scotch bright to get it nice and clean before reinstalling the TB with new gasket.

Do you know the appropriate gap size between the plate on the butterfly valve and the TB body, I want to put a feeler gauge in there and make sure that it is appropriate.

Here are some pictures that I just took, please dont mind the wire mess, The 86 engine bay did not have all the metal bracketry to connect all of the 88 wires and relays and stuff, fixing this is a future project of mine,, right now zip ties are my friend. Let me know if you see any potential problems[/QUOTE]

The torque on the TB gasket doesn't matter. Just tighten it. Don't snap the bolts. kiethmania is right on, and he's talking about your intake manifold gasket, which is soooo easy to screw up. And by screw up I'm not busting balls, I'm just saying the first time you do one, your pretty much apt to make a mistake.
1. Did your high idle occur after you replaced your intake manifold gasket? 2. Can you hear any hissing sounds?
Best trick I've found for sourcing vacuum leaks is a piece of rubber tubing placed in your ear. Run the other end around the intake manifold edge where it meets the head. I bet your hear a hissing, and you've found your leak. But guess what, once you do this, you'll find a couple more I'm sure. Have fun and get ready to swear alot..

I did replace the manifold gasket and I used the Factory service manual's recommended torque sequence and torque specs, I checked the torque on every bolt at least three times. Someone mentioned the smoke method, did you use a large size vacuum tube to run to your ear? Also someone mentioned spraying starting fluid and looking for bubbles and listening for idle increase. I don't really understand how you can screw the manifold gasket up, there are alignment pins to put it on and everything, don't get me wrong it's a big job but not hard at all, I did not want to tighten the bolts tighter than recommended specs because i didn't want to break one off. I will double check all of the torques and try to spray something on it to look for bubbles. Does anyone know where I can get a smoke machine, i dont want to use a cigar, I don't smoke and wouldnt be able to keep it lit. I wonder if an incent could make enough smoke. Could you tell me how people usually screw up the first time they change the manifold gasket?

Oh and the reason I changed the gasket was because of the high idle.

As for the clearance between the throttle butterfly and the throat of the throttle body, the answer is "none". That bolt is to keep the butterfly from wearing the bore-only. No idle air is to pass by the butterfly. The idle air is adjusted using the torx bolt on the driver side of the TB. Yo umay have a small expansion plug covering it if it's never been adjusted.

I guess what I was meaning is the actual circular blade that flips open and closed with pushing the gas pedal. When I hold the throttle body up with light behind it I can see light all the way around the metal blade, which is what I am referring to as the butterfly. Should I see light between the circular blade and the concave portion of the throttle body? If so how much

I would imagine that a great bit of air is passing around the circular blade that I am referring too.

I just found this picture I took when i had the TB off. does this look normal, with that light shining through, i would imagine a ton of air could pass through there. This pic was taken with the TB completely shut.

There ya go. Shut the butterfly. It's way too far open. Shut it so the adjustment screw isn't affecting it. Then turn the screw in just til it barely quivers. Stop there.

Do you think that this leak is allowing enough air for a 1600 RPM

Yeah thats not normal. Check for a mechanical blockage in the travel of the butterfly. Adjust as crusier54 stated. The size vacuum hose should be around 1/4 inch. Smoke machines are the shit, they pressurize your intake with smoke, and you can see the leaks. There expensive, and pretty hard to make at home. The TB cleaner/brake cleaner method works, but only on huge leaks that you should be able to hear already, I've tried it several times with no success. As far as how you can screw up an intake manifold gasket: When you get your idle back down, try the vacuum hose technique for giggles. Its not so much that you screw it up, its more like how did the manufacturers of the gasket you used screwed up. I've seen two gaskets out of the box be crap, one gasket was "made" for a 99, but was clearly for the 98.

truck7575 said:

Do you think that this leak is allowing enough air for a 1600 RPM

Click to expand...

Yup. One way to be sure. Adjust it likes it's supposed to be adjusted before spending one more second searching for other answers/solutions.

650 RPM never sounded so good I had to adjust the stop screw almost 3/16 of an inch to get the blade to sit flush. It looked like someone had adjusted the stop in the past cause part of the threads were corroded more than the ones closer to the throttle body. Thanks for all of your help!

good stuff.

Glad to hear you got it fixed.