You need to find out what codes are in there. Before you can troubleshoot po420, (which it sounds like your describing), there are about 20 codes that CAN NOT be present, before troubleshooting this code.
IF that is the only code, than you need to check for an exhaust leak at the O2 sensors or any up to the engine. Excess oxygen throws out the true readings of the gases by the O2 sensors.
Since you say that "sometimes" you have the power you expect it to have may mean the converterter is broken intrnally and intermitantly plugging up.
So find out the codes.
Thursday, April 19th, 2007 AT 6:02 AM