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Boy, I am surely sorry that you are having such a terrible time trying to choke the life out of your engine! (:-)
I have used those hose stethoscopes but mostly for metalic sounds and pressure leaks.
I likes, being blown in my ear, as it tickles more(:-)).
In reading you explanation of ruling out the cabin climate control vacuum bottle, I almost got confused myself of which way you "mouthed off" opon that "little" hose.
I believe you sorted it out and you do not have a problem there. Besides you blocked all of it off earlier.
The check valve will have the white side (the vacuum bottles color) sticking away from engine. This way it allows air out of the bottle and you should only check those things with a vacuum because the seals in the control box and bellows are made to hold vacuum.
With pressure the bellows might rupture.
The Seals themselves need to slip and slide on surfaces. These seals allow air into enter the bellows of those and vacuum motors to equalize. The status of usage could be used on one or the other side for vacuum but at different times at atmospheric pressure. No PSI's were designed in.
I prefer to watch a hand held vacuum pump with a gauge.
If you had a very small leak, you could be hanging over the fender for sometime waiting for it, wet tongue and all.
There you are with a tongue stuck tasting some stale rubber or the other persons beer as pressure puts things in stuff!
Guess there are those brave, he-men types, everywhere!
There is some internet verbage out there about why men don't live so long, that is quite funny, to me!
Yours, goes back to us all being boys I'd say! (:-)
I am not familiar with an 88 but on my 86, you might have the ICU on the washer bottle fender. It was mentioned by another poster but stated the distributor. That is not the right place.
There should be a white nylon line connected to diaphragm that runs under the engine to the ICU and BACK to a port on the intake manifold that hooks to a fitting under that familiar (:-) climate control vacuum line.
Some people do away with that line thinking it helps with emissions. I cannot support that idea as I have no idea but figure some smarter than me put it there.
Is that fitting plugged or a solid connection without leakage of the diaphragm? It controls timing, under load, I believe?
You should only a hold a vacuum on the Fuel Pressure Regulator intake manifold connection onthe housing and definitely no gas from it either!
With evaporative canister and flame trap lines plugged off that leaves air only through the throttle plate, the mixture screw that is worthless on the LH and that electronic controlled IAC valve.
Considering that you have the throttle plate centered in the bore and resting only in the bores center circumference without the outer shafts lever, sitting on the stop screw holding the throttle shaft and to make all the air where it can only go through the IAC! This we want!
There can still be a minuscule amount of air sneaking around the throttle plate because, after all, its only a squared edged metallic plate is doing the sealing. Air is darn thin too!
It is not enough air to run the engine and this is good. We want that amount of air to be below or at the most closed range position of the IAC. The IAC will then have to open slightly to get the engine into a smoother idle and then move it on up to a specification set by the ECU's fuel management program.
You should never hear a stumbling or racing engine when its dialed in with the other components. It should rev up to start and idle right back to specs. If it does not, suspect the IAC!
The IAC must be set to have enough RANGE to thin and enrichen air flow under all conditions.
The IAC SYSTEM must deliver this to work on a mass produced engine, run with consistent reliability of performance, within a framework comprised of a less knowledgeable public arena of owners and of course, still studying (on your hourly dollar) mechanics!
Fuel mileage is affected more by bad ignition maintenance, a bad fuel pressure regulator or the O2 sensor. Other things are short trips, road conditions or even more likely a lead foot on the pedal and I should have left sooner!
In the book they want you to believe that you have to set the stop screw open a certain turn amount and the engine run at certain RPM. This is not so as smooth is option or actually not required!
You want it to barely rock the plate open or as I do it, I feel it touch the lever and give it one- sixteenth to almost one-eight turn and lock the screw down. Do not look for or expect space around the plate as you are not suppose to see any!
Seeing any is too much, unless you have a light behind it and left it on inside the engine!
Do not expect expect really smooth because the IAC valve will do that when you unleash it by removing the ground.
The stop screw safe guards against jamming the plate in the bore from the return spring pressure and a quick or hard release from wide open throttle position.
This leaves only the IAC to let the engine breathe and maybe that Mickey Mouse plastic air screw but do not count on it on LH systems. Those are left over K-jet parts. Its Like, the saying, its cheaper to keep her, I mean, IT, as mid-production changes, are like change orders, when building a house!
If you cannot get it to idle after that then there is something wrong with the IAC or the IAC is being told to do more RPM by the ECU.
Just like recently on ENGINE 41's car it turned out to be the a/c thermostat switch in the dash, was accidently turn on since one of the Bushes administrations.
The micro-switch attached, which was an auxiliary device to tell the ECU to hold the idle higher for the additional load.
On the 91 models all of that stuff has been removed and done closely in conjunction with the ECU/IAC the same way.
If you got that puppy choked out, it has be the IAC or a very well controlled intake manifold leak, IMHO.
Phil
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