i have a 52plate 1.8, and the catalytic converter light has come on. when i'm driving along for the first ten mins its fine, but after that its a different car.

Before it came on it would accelerate at the slightest touch of the pedal! Now it judders in first an second, an i get no power at all till 3000 wen the other cam starts working.

Then crusing in fifth at 70-80 it will slow down an not maintain the speed unless my foot it on the floor!!

Also when starting up after its been sat for a while (overnight) it revs to 2000 then drops down to normal, then down to about 300rpm, back up to 2000 for a second. So it does this for 5-10mins until its warm then its ok!

Anyone have the slightest idea why?

I use redex regularly, and i changed my spark plugs cos i thought it was them, i cleaned the throttle body too.

HELP

cheers!!