Low Power Problem — When engine is cold and I go to accelerate from stop I have very little power (cannot get over 25-30 MPH — If I mash on the pedal it is worse). If I keep my foot pressed on the accelerator for about 1/2 - 3/4 of a mile the engine finally "kicks in", but if I stop and start again then the whole process starts again. When the engine is warm the problem is not present and I have fine power and acceleration.
I had a mechanic replace the Air Mass Meter but still have the problem. O2 sensor checks ok, and the fuel pressure was checked overnight and tested good. I would appreciate any input before I go any further with costly guesses.

Idle Problem — Engine idles very rough. In park it dances above & below 750 RPM; in Drive it dances above and below 600 RPM. Mechanics cannot get it smoothed out. As a result I am having exhaust system problems and the car's baffling is coming apart ,which is extremely noisy and irritating, from the excessive shaking and rattling of the engine. Any thoughts? Thanks