Erratic Boost and other odd behavior

[tpboyce]

A little history:

Car is a 2001 Pontiac Grand Prix with 58,000 miles. Majority of miles were put on with 200 and 500 mile round trips on weekends. Car had been running great, with only major maintenance being a tie rod end from a pot hole and the valve cover gasket replacement under warranty. Noticed a slight odor of antifreeze coming from one of the two cars. Eventually saw a tell tale puff of steam from under the hood of the Grand Prix. Took it into local mechanic who is usually pretty good. He replaced the intake manifold gasket. Upon receiving the car back, was running great until I took it on a longer trip. On the way back, the Boost indicator would come on when I was decelerating. Car was also acting a little erratic. Took it to the mechanic who did not find anything. THe next trip left me stranded at the side of the road. Car stalled and would not restart. Mechanic towed it back and said a vacuum hose had collapsed. Next incident was a fast idle. It has been in the shop 7 times for either stalling and not restarting, boost light comming on when decelerating, very fast idle (3000 RPM). Also has rough shifts. So far, Mass Air Sensor, Throttle Position Sensor and Oxygen sensor have been replaced. I am able to reproduce this behavior on demand after picking up the car, however, dealership and local mechanic always hand me the keys and say they have fixed the problem. Dealership now wants to replace the computer. They say that they swapped in a computer from a used car on the lot. I really do not think it is the computer. I think the mechanic missed something when he did the intake manifold. Any thoughts on what it might be?

 

[gtpinsc]

its a vac leak... trace all vac lines pay close attention to the t boot under snout of supercharger and the fitting that goes onto MAP sensor.

 

[gtpinsc]

could also be the boost bypass valve...

 

[Rather B Blown]

sounds like a vac leak..mine was doing all that fun stuff, and i found that the T under the s/c was in pieces. I couldn't buy one anywhere cause nobody sells them, so i taped it up really good with electrical tape and its been fine ever since

 

[gtpinsc]

sounds like a vac leak..mine was doing all that fun stuff, and i found that the T under the s/c was in pieces. I couldn't buy one anywhere cause nobody sells them, so i taped it up really good with electrical tape and its been fine ever since

this.... lol i just re-taped my T for the 3 rd time. i can always tell when it needs to be re-done..... start to have long shifts due the leak messing with throttle position sensor.

 

[SDGTP99]

sounds like a vac leak..mine was doing all that fun stuff, and i found that the T under the s/c was in pieces. I couldn't buy one anywhere cause nobody sells them, so i taped it up really good with electrical tape and its been fine ever since

Oddly enough you can buy a metal or plastic T-Vacuum lines at PetCo. They even some sleek shiny black tubing you could use for the vacuum lines. All located in the fish section. :th_winking:

 

[blueguy]

this.... lol i just re-taped my T for the 3 rd time. i can always tell when it needs to be re-done..... start to have long shifts due the leak messing with throttle position sensor.

Jesus broke ass...buy a new set from the DEALERSHIP :th_nanana:

 

[98GTPCALGARY]

Oddly enough you can buy a metal or plastic T-Vacuum lines at PetCo. They even some sleek shiny black tubing you could use for the vacuum lines. All located in the fish section. :th_winking:

I dont know if that would stand up to the heat very well, but I love the idea of getting car parts at a pet shop, lmao

 

[gtpinsc]

Jesus broke ass...buy a new set from the DEALERSHIP :th_nanana:

this was kind of a douchey thing to do but..... i went to stealership to get my PCM flashed back to stock cuz my tune was messing with trans. well they quoted me a price and after they flashed it... the service advisor tried to pull some **** and tried to charge me like 50 bucks more than quoted.... all i had was the amount quoted.... so i was like i have to go to the ATM and get the rest.... i left and never went back... :th_nervous: so i stay away from my local dealership. :th_nanana:

 

[tpboyce]

its a vac leak... trace all vac lines pay close attention to the t boot under snout of supercharger and the fitting that goes onto MAP sensor.

Okay, I traced all of the vacuum lines. They all appear to be good, actually better than I thought. The one going into the MAP sensor which seems like it is a snap on/swivel type of connection is not necessarily a snug fit. I thought about taking off the Boost Valve, but was a little hesitant.

Dealership is insisting that it is the computer, but they will not guarantee it. Special ordered electronic part, once we install it, you own it. There are no gaurantees, other sensors that were bad but not reported bad by the old computer could show up. Sounds like an open check book to me.

Someone on another forum suggested a ground might be missing as well. Any ideas what grounds I could be looking for?

 

[gtpinsc]

dealerships are pretty much retarded.... does trans shift at right?

 

[tpboyce]

Trans does wait to shift when it is acting up. It does not act up all of the time either.

 

[gtpinsc]

still signs of vac leak... vac leak will cause codes for all the sensors u have replaced also.
does it feel like a long drawn out shift? maybe ur mechanic sucks and intake gasket is leaking.

 

[tpboyce]

I was kind of thinking a manifold leak myself originally based upon the pattern that needs to be followed to get it to happen. I have to get the engine up to tempurature, stop and then drive again. This had me thinking that maybe something is loosening due to tempurature changes. Thoughts on how I could check for a manifold leak? Would just using starter fluid around the flange do the trick? I probably should have never taken the care to the stealership because we have lost a accountability. At one point in time I told the mechanic to tear it back down to the heads and put it back step by step according to the manual. He did not do that and returned the car to me changing the MAF and saying he was certain that was it.

 

[gtpinsc]

theres a write up on LIM change... its kinda timely... but if u have tools and mechanically inclined u can do it urself... may even be supercharger gasket messed up... id almost put money on it that thats ur prob. one of the 2 gaskets.