Vacuum leak?

I've been having a problem with my 2000 GTP for a few weeks now. When I start it up it has a rough idle and every few days or so it will die while its in idle. Also when I have it in WOT the boost gauge only goes about half way up at the most and there is a noticeable decrease in power as well as a slight "whistle" noise coming from the engine. I'm also noticing a drog in my mpg. I'm thinking it might be a vacuum leak but I have no clue as how to check for one or go about fixing it, any suggestions would help.

check right below the supercharger on the left, there shold be a small hose coming off of the upper intake, then follow the little black hose, if broken, just get a little rubber peice to connect it, other wise it could be the mass air flow sensor on top of the throttle body, i had a vac leak too, no big deal and little T line fitting from any store should help i can get pics if you need it

Any codes?
Maybe suspect Cat.

cat wouldnt hurt the idle, to my knowledge, it could be a vac leak or a MAF sensor, pray for the vac. a maf sensor is pricey

Thanks man i'll go check it out, and yeah some pics would help out. Thanks.

ok ill be right back.

Most big losses in power have been Cats. And his being 8+ years old....
I would take off each vac line and inspect for cracks at connections.
Clean your MAF with some MAF cleaner, or CRC cleaner.

Sorry for the double post, I forgot to mention i replaced the MAF sensor about a week ago to try to solve the problem becasue i had a P0102 code for the maf, but after replacing it the code was still there and it didn't fix anything.

Check vac lines, then I would get cat checked out.

Alright, I'll start there. BTW 20gtp02 you just made me decide to get my windows tinted, my car is the same color as yours. The window tint does a lot for the looks.

alright here they are


^^^ mine broke a week ago and had terrible idle/boost



below the snout


^ check the vac. tree as well and just fallow along the line

That was my first mod! 15%

Unlikely that it is the MAF, I doubt it's the cat but it may be. If it is you normally don't recognize any problems until 4000 rpm. It will fall flat on it's face and you would smell gas when entering/exiting the car.

I would suspect a vacuum leak as well.

An easy way to tell if you have a vacuum leak is to take a spray bottle of water and squirt all your vacuum hoses and where they connect, you'll hear it suck in the water and you may even see it bubble.

Also spray around the base of the supercharger where it bolts to the LIM and spray around the throttle body area, a leaky gasket can also cause a vacuum leak.

Edit: Also, check your BBV, that may be stuck open, not allowing you to build full boost. It is also vacuum operated.

i have little connector everywhere, BTW you can buy vac. kits at a GM dealer for about 30$ , otherwise be careful theyre brittle

......well i checked the area for a vac leak, and there was a section pulled out from one of the vac trees, I pushed it back in a ran checked for anything else, but while doing so I accidently snapped the line. I took it into auto zone to try and find somthing to connect it but I noticed that although it was cut in half I had gotten my power back and and I could get full boost. I went into autozone and connected the broken line with a rubber connector he had given me but when I took it out to drive again I had lost my power and I was getting a terrible idle again. I pulled into a gas station and checked the connect but while doing so I accidently snapped another section of the darn hose and now there is a huge gap of hose missing. I drove it home and once again I noticed I had a bigt increase in power again, when stopped at a stop sign or street light it would want to die when I tried to get going again. I can get any replacement tubing right now because the GM dealership in my town closes at noon. Anyone got an idea of what i can use as a temp fix until monday? I can post pics of what I'm taking about if you need them.

just get a really tight fitting vac. tube, yea i knew it was a leak, but i told you be very careful when playing with these lol

lol yeah i know, but i wonder why i would get my boost back after i broke the line. Seems strange.

probably somehwhere in between there, i dont know but if the T line is broken off the manifold then there wont be much boost, these break all the time, but too much boost can make that thing crack and break lol its sounds pretty BA lol

what vacuum line broke? do you have a picture of where it starts and ends?

you can in a pinch use windshield washer tubing, you can get that at Autozone as well, just replace the whole line.

What section is broken? I'm sure you could make something work, they sell rubber line at Autozone that you can make work when you're stuck.

I know a lot less than most of these guys about this subject, but when was the last time you changed your pcv valve? My GTP was doing the same sort of things before I replaced mine. I would only run ok if there was a vac leak, but if you fixed the leak it would go to hell again. A new pcv for about 5 dollars fixed it.

.....well i bought brand new vac lines and replaced them yesterday and now I'm back at square one with the exact same problem. I might try replacing the pcv valve tomorrow to see if that may be the problem since its a cheap fix. Anyone have any other suggestions in case it dosnt help, i'll get it scanned tomorrow as well and see if any new codes have come up.

Edit: BTW when im at full WOT when the RPMs start getting pretty high I can hear a loud whistle noise from the right side of the engine

Right side when you're facing it? Do like Randall said and mist your intake with water, see if you have a leaky gasket.

the noise is coming from the right side when i'm driving it, so it would be the passenger side.