I have already spent most of a day searching through these forums and my car and I have not managed to find my problem.

The car is a 1990 GTA with a TPI 305 and T5 trans.

I have a vacuum leak (at least I believe it is a vacuum leak--I do need to rule out the EGR valve and perhaps the IAC) which I can hear as a whistle when vacuum is high and the car is hot. I only hear it when I am decelerating, and the car must be hot. I don't hear it if the car is still cold. It is not present at idle. Of course, this makes locating it that much more fun. I have been all over the engine with both an unlit torch and with carb cleaner (avoiding the distributor/coil with carb cleaner of course) and have found nothing.

It is overdue for emissions--overdue on account of my inability to nail down this gremlin. I decided to try taking it in anyways just to get some readings, but the tech wouldn't even test it for fear that it will get a gross polluter reading. He did put it on the treadmill and found that it has a miss under load around 2000 RPM. He suspects plug wires for that. He did not experience that vacuum leak. I am rather dubious of the plug wires being at fault, but I picked up a set and will change them. That's not a big problem. Whatever is causing this whistle is driving me up the wall. The car does smell rich at times, not just during warm-up, but it doesn't always smell rich.

Other details: The injectors were recently (within 2 months) sent out for cleaning, received back and re-installed. That was done as a response to my discovery that the fuel pressure diaphragm was breaking down. Diaphragm replaced and stock fuel pressure regulator re-installed (aftermarket unit would not hold its setting). I was hopeful that the vacuum leak would go away with the replacement of the gaskets for the intake runners, but no luck.
The intake to head gaskets are not showing any sign of a coolant leak (my experience has been that the coolant passages are the first to go) and I have put plenty of carb cleaner along the top edge of the manifold. Of course I cannot test the valley side of that gasket.

Any thoughts?

 

Pinched off the brake booster line recently?

 

Brake booster line is in excellent condition (I think I replaced it when I rebuilt the motor 5 or 6 years ago) and a quick pry at the booster fitting shows that it is still holding vacuum with the engine off.

Given the above would you still regard the booster as a candidate? Do they have a reputation of developing leaks in this manner?

I have replaced the plug wires and have no appreciable difference in the picture. I can smell that it is running on the rich side. It may be a little better under load, but nothing to get excited about.

 

Morraine boosters are fairly reliable. I only asked in case you overlooked it.

Do you happen to have a vacuum reading at a given RPM?

 

Thank you Vader for following up.

A quick vacuum test has it at 18.5" @ 750 RPM, 19.5" @ 1000 RPM and 18.5" @ 2000 RPM. This is with the car parked and relatively cold.

I want to hook up the vacuum gauge so that I can drive the car with it and see what it is doing when hot and decelerating in hopes that I can figure out what vacuum needs to be in order to reproduce that whistle. I don't have the right vacuum tee on hand. I will get those numbers Monday or Tuesday.

I am also trying to put the pieces together so that I can figure out what the computer is reading from the sensors. I have an old laptop that needs a battery, and I need to get a cable on order. Hopefully I will be able to pull some useful information out of the car.