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Hi, most if not all of the rubber diaphragms have a hole in them after 35 years.
Vacuum is applied to the diaphragm until the coolant temperature reaches 140 degrees, any higher and the vacuum is closed off and the spring forces the plate open.
With that in mind, the rip or hole in the rubber will create a vacuum leak until the engine temp reaches 140 degrees.
You will never find this leak on a warmed-up engine!
There is a simple test in the FSM for this.
There is a thread for substituting a new EGR diaphragm in place of the old leaking one.
I will be forever grateful if I could get a couple links or a little bit more description? I’m right there on board with the idea we have cracked rubber somewhere. Especially just sitting for so long with upstate NY winters and summers.
Thanks for the heads up on the brake booster. I have one more thing to check now. The double throttle diaphragm, the EGR, BAC and maybe the ACV leak without visible smoke. My AVC was leaking at the sensor so, that was visible. There was another that I helped with ended up being freeze plugs. There at at least three in the intake, maybe 4. Two of which would not be visible.
I had small leaks from a couple of those and I still could set idle speed, it was a bit low but manageable.
So with the flap open, it simulates more air getting in, therefore there is to much gas? or not enough air? or both? Or a broken AFM or to much air already?
the more air that passes through the airflow meter the more the flapper door opens, when the engine first starts there is a surge of air and the door opens a bit but then is closes as the engine idles back down. if there's air leaks the door will close too much to the point the fuel pump switch opens and shuts the fuel pump down and the mixture leans out too much. closing the screw on the airflow meter forces more air to go past the door and manually force it to open more, richening the mixture and forcing the fuel pump switch to stay closed and on.
it's mostly a telltale of a large vacuum leak somewhere in the system, but if the airflow meter is worn or defective it forces it to run the engine in a richer part of its range, an engine can run rich just fine but it will not run lean very well if at all.
manually opening the door with your hand or screwdriver simulates this.
low fuel pressure can also explain this symptom, you guys should also be adding that to your list or checks.
Last edited by notanymore; May 13, 2025 at 06:36 AM.
Yep. All makes sense. I'd like to see if I can find the vacuum leak instead of messing with the air/fuel mixture. But so far smoke test isnt producing anymore signs.
A little more clarification on 'gsmithrx7's post-- regarding double throttle vacuum leak the fixing or replacing the EGR diaphragm is now on my hunt.
Of course I had that realization that its most likely something I should've done when I took the intake manifold off earlier in this project.
But now that I have a little practice, its not the total end of the world if I have to do that again.
Or maybe adjust the air/fuel to get it running for the summer and tinker with it next winter!
You are in luck. The EGR vacuum solenoid can be easily capped without much effort. And the same with the double throttle. If the check valve is good on the double throttle diaphragm hose, just flip the hose backwards and it will cap off the connection from the thermowax. My hose did stretch when removed so, it may not work well.
You are in luck. The EGR vacuum solenoid can be easily capped without much effort. And the same with the double throttle. If the check valve is good on the double throttle diaphragm hose, just flip the hose backwards and it will cap off the connection from the thermowax. My hose did stretch when removed so, it may not work well.
oh good. I was worried about having to remove the intake manifold. I’ll start searching for capping the egr and checking the check valve. I’m sure it’s on this forum somewhere. lol.
Tempted to make her run a little rich to see if the flapper door stays open.
Dumb thought/question, can I weld or tack something inside to keep the flapper from closing all the way too?
Duct tape fixes everything!! It would stay open though. The key is how far.
As far as I know the flapper moves based on the amount of air being pulled through the intake, it varies based on engine speed/flapper position and sends information back to the ECU. That's why you tested the pins with the ohm meter... with the flapper fully open and fully closed, right? The signal needs to sit in a certain range because the ECU is tuned to interpret the signal in a specific range.
The amount of suction from a running engine is a bit surprising to the uninitiated.
See the green broken piece.. that is for the double throttle hose. It is a one way valve in the green part, cap off this port in the rear of the throttle body or if the green part holds pressure, reverse the entire hose including the green part.
The EGR solenoid is Orange. There is a very short hose to the rack.... block off the nipple on the rack that goes to the EGR. The EGR is under the intake, very close to the solenoid rack. There are other hoses there at the solenoid and rack, so chose the correct one.
Unless you have a massive leak in these places, this will likely not help with the leaking much. Both of mine leaked a little bit.
Edit: I forgot to mention I am not sure the EGR solenoid is even activated at idle. And I can not remember if that solenoid is normally open or normally closed. Probably normally closed?
That flapper door AFM does have a thing in it that when it starts to see airflow, it will close the switch that turns on the fuel pump, you might need to take the black plastic cover and see if it is closing the switch
That flapper door AFM does have a thing in it that when it starts to see airflow, it will close the switch that turns on the fuel pump, you might need to take the black plastic cover and see if it is closing the switch
Yep. Already been there. I was just bored one day and pulled the lid off and inspected the connections inside. The bar makes contact when closed and will stay open when the flapper door opens. But as soon as we lose air/vaccum, that door shuts and the fuel pump shuts off.
So all signs are pointing to a vacuum leak causing the continuation of air while at idle to continue.
I just havent had time to review the messages about flipping hoses and blocking stuff off yet.
Thats my next step.
Plan B discussed is increasing the fuel mixture to run more rich, thus to require MORE air to get sucked in and hopefully keep the door from closing all the way.
Yep. Already been there. I was just bored one day and pulled the lid off and inspected the connections inside. The bar makes contact when closed and will stay open when the flapper door opens. But as soon as we lose air/vaccum, that door shuts and the fuel pump shuts off.
Slightly confused by this statement, when there is no airflow and the door is shut, the arm of the sweaper should press against a small piece of metal, opening that switch, and when there is airflow, and the sweeper arm moves, the spring loaded switch should close, sending power to the fuel pump.
Video attached showing proper motion for confirmation:
If you are looking into the plug on the AFM, and hook a multimeter to the two left most pins, there will be no connection with no airflow, and continuity when airflow and flapper door is opened.
So I just watched that video posted and noticed a difference between that and what’s on mine. The gap when open/close is much larger. Mine was micro/small when separated.
Like, a couple sheets of paper width.
I should do a poll:
Just try and get another MAF sensor and see or B) keep chasing vacuum leaks?
i gave several steps to verify that, jumpering the yellow fuel pump test connector or measuring voltage at the pump itself, i posted the wire colors in another thread here:
a slightly simpler explanation of the air bleed adjustment screw on the airflow meter is this, by turning the screw out it allows more air to bypass the flapper like driving on a frontage road to avoid a backup on the freeway, making it open less since not all air is pushing on the door. screwing the screw in fully makes ALL air have to travel through the flapper and in effect open it more, having the double effect of ignoring medium size vacuum leaks/keeping the fuel pump on and telling the ECU the engine needs more fuel.
Last edited by notanymore; May 16, 2025 at 08:58 AM.
If you decide to change that air bleed screw, mark it, and then tighten it down, counting rotations, so once whatever leak is found, you can return it back to stock by tightening it back in and then going out that many rotations back to the mark you made.
Yep. You did. I was just hoping it would be a last resort to adjust that screw. But I think that's gonna be the weekend steps. Get a marker. Count turns etc.
I'll update with some hopeful positive results!
Thanks all.
Well, I hate to admit this, but I think I made an error when putting the intake manifold back on.
I cleaned off the old gasket and everything. Slapped on a new gasket and put the manifold back on. Well, yesterday I had a couple of car guy friends over and we were working on the car. We fired it up (with me holding the MAF door open manually) and really just looked and listened.
There's a distinctive whistle of air on the passenger side. Having a few extra sets of eyes and ears helped.
Then the one guy said to me "When you put the gasket on, did you use any sealant? I think that's your vacuum leak".
I of course just blinked when I realized. Never even occurred to me to put down some sealant.
So I'm thinking thats where I'm headed next. Pull off the intake manifold again (already got some practice)
Question/Thoughts: While I'm at it. Should I use that opportunity to get a block off plates for the EGR and that little antifreeze/coolant thing? Or would that be another change that we just dont need to add to the mix at the moment?
You shouldn't need sealant. It is nice to have because the gasket won't stick to the metal. The surfaces need to be cleaned very well though and the bolts torqued. As far as the path forward, I am not the person to ask. I have a tendency to overdue it.
i don't use sealant either, but i could have sworn i heard the whistle in the video as well, you can hear a hiss from the throttle body but there should be no whistling type noises.
It would stay open though. The key is how far.
