Hey guess I know this isn't the forum for a Regal but I have a GP also. Since the Buick and GP use the same powertrain I figured I might get some help here. I have this 2003 Regal (101,000 miles) w/3.8L engine and 4T65E transmission. At first the car wouldn't go faster than 40 mph and now it doesn't even want to idle. I was told that it needed a catalytic converter so I disconnected the pipe just to see if it would idle a little and no such luck. So I am ruling a converter out. I pulled the throttle body off and the inside of the intake has melted a little. I also noticed what looked like a little bit of anti-freeze inside the intake. Would a little anti-freeze leaking into the manifold cause the car to act like it needed a converter and cause the loss in power?
Is there a sensor on the motor that could cause this problem. My 2000 GP did the same thing and I continued to try and drive the car until it started to knock. Well I replaced the engine and have been driving it since. Someone told me it needed a converter too and that tuned out to be false.
Any help would be appreciated.

It does sound similar to the intake gaskets going. With the cat disconnected, pull your injectors fuse, take all your spark plugs out, and crank the engine over for a while. This will get most of the crap out of your cyclinders. Clean the spark plugs extremely well (torch them for a while if you can), put them back in, reinstall injector fuse (leave cat off... doesn't matter). Try to start it... if it starts and dies shortly after, you know you have coolant leaking into your intake and the gaskets are the problem. The lower the leak, the longer the engine will run for.

Hey thanks for the info zuulmusic. I plan to replaced the lower and upper intake gaskets this weekend. That's a nice GP you have. I plan to get mine repainted after I replace my carpet.

the leak might just be coincidence and your real problem might be your MAF. try disconnecting it and see if it idles better.

Well I found out what the problem was with the Regal. The plenum had a hole burned through it. Don't know why it happend but as the hole got bigger the car ran worse to the point it wouldn't idle. I have never seen anythng like that before. I would post a pix of the plenum but not sure how to upload it here. I guess the guy who put the car on a machine and it said replace the cat needs to get a new machine. Well this was diagnosed at a stealership. Thanks for the input guys.

http://www.grandprix.net/ubb/ultimatebb.php?ubb=get_topic;f=5;t=001572#000000

for the write up on posting pics. Really isnt all that hard. Welcome to the site. I sure hope you enjoy the stay. Try the veal.