Thread: HELP!! No power and bad idle

From a dead stop it does this?

How high are the rpms getting before you move?

clogged cat?

My bet is "Five Finger" is "spot on"..........I've got the same problem going on currently.......no power and yes, bad idle..
I just got my 00' GT (105k) on the road and I just replaced the upper plenum also as I saw oil drops in the coolant. I hadn't run the car before that as I just bought it and it had been sitting for awhile. Once I got it on the road, it ran okay, but not great.......a slight lag or hesitation on acceleration from a dead stop, which I attributed to it sitting so long prior to running. I had changed the plugs at the time I did the plenum work. As I ran the car it got a bit better, but I started to hear pressurized air blowing on acceleration, almost like the sound of a turbo, which I'm familiar with.
I only ran the car one more time since I heard the "rush of air" sound and I decided to investigate. Popping the hood I found where the "air injection check valve" had cracked in half at the lower body, and that the plastic top/cap of the vacuum diaphragm was completely melted. The inner part of the valve was splattered with flakes of molten aluminum where it obviously melted the lower part of the valve. I got lucky as the hot gases also melted the corrugated covers of my fuel lines, but never touched them (yeah, they run right over the top of the valve that self destructed).
Anyway.....long story short......I replaced the valve, tightened everything back up and replaced the gooey pieces, only to find that it now runs like crap.........very doggish and won't accelerate worth a damn.......and it get's hot in the engine compartment, but the water temps are normal. A short run of a mile & back leaves the converter ticking like a clock.....HOT.
A no brainer..........plugged converter. I would've never known it unless that valve let go because the exhaust had a place to vent, leading me to believe that the slight acceleration problem was something different. In my case, the plugged or congested converter caused the hot exhaust gases to reroute and over heat the check valve trying to work back upstream towards the air pump.........basically pressure, and hot pressure at that.