Idle trouble in my '93 Dodge Stealth

hi! I have a 1993 Dodge Stealth (3.0 V6 SOHC) that has been idleing a little rough, especialy when the a/c is on. It was suggested to me that a dirty throttle body could be the cause, so I cleaned it. After I did that it ran great with the exception of idleing around 1000 RPM insted of the usual 300, then the next day driving home from work (ran fine on the way TO work) whenever I tried to coast or engine break my engine began to shudder and run really rough! any ideas of what could be happening?

I also just discovered that the engine wont rev over 4500 RPM (it redlines @ 6000), if that helps.