I have changed out the plugs with AC Delco Iridium plugs, and new lifetime warranty 8mm plug wires. I also removed all three coil packs and had them checked out. All three are in good shape. I get a code that comes up "exhaust inefficiency". So now, with the blower belt removed, there is less air going thru the exhaust and the shudder has gone away. Has anyone replaced their cat converter and resolved the shutter?
The code that pulls up is number 0420 "catalyst system low efficiency". The local parts store doesn't know what this means. Anyone know?
