I have a 98 Malibu LS 3.1V6, the car will not idle when in park or nuetral. The rpms consistently jump from 500rpm to 1100rpm back and forth and will sometimes completely stall out.
Also, only when the car is cool, it is somewhat hard to start. It only wants to start if I tap the throttle. Then, once started it runs very rough, like a severe misfire. But once I rev the motor up, it clears out. It does not do this if the car is warmed up.
If the car is in gear, it will idle just fine. And the car seems to run and drive normal going down the road. No actual misfires.
The check engine light is on. It is showing codes P0300 (multiple misfire) and P0401 (EGR flow insufficient). The plugs and wires look good, I have switched out the coil pack with a known good one, and put a new EGR valve on. No changes.
I dunno what to do next, I am suspecting the catalytic converter. Seems to have a foul smell from the exhaust, and a puff of blue smoke at cold startup leads me to believe possible worn valve seals may have caused failure of the cat.
What you guys think