Slight Misfire On My 2.0 Dohc

[Galdabla]

Four weeks ago the wife arrived home with a completely burnt out Secondary air injection switching valve. Tuning garage said Cat had gone and exhaust gases were looking for means of escape hence the burning.

 

I've replaced the Cat, and put on a 2nd hand valve and air injection pump.

 

I've replaced the plugs with correct gaps & HT leads hoping that I won't have same trouble. Also replaced Air, Oil & Petrol filters.

 

She runs much better, more power but there is still a misfire at low speeds.

 

Now booked in for a diagnostics next week because I don't want to throw anymore monet at it and trying to guess what it is. Any idea anyone?

 

ps - I've tried previous threads but can't spot anything.