I recenently had my 2002 Focus to the garage as the engine management light was on
They did a Diagnostic check and came up with the Lambda sensor was at fault which they replaced.
They then said it was still miss firing and after checking plugs etc they came up with the Mass air sensor was required as they said it ran OK when it was unplugged.
I ran with it unplugged and it was a hell of a lot worse than when I had taken it in so I pugged it back in and it then ran a lot better Not perfect but better, and the management light was still on.
So I think I might change the MAS myself as I feel the garage were charging over the top and if I can get the part number I can get a MAS from our car dismantlers
DUMB QUESTION where can I get the part number from ???

 

Have you tried reading the part number off your MAF? (oh its MAF btw before you get parts guys looking at you funny lol)

Did the garage not clear the fault codes after they replaced the Lambda sensor because that will need doing?

To be honest it sounds like the MAF is working otherwise it would drive the same if it was unplugged or not. If its ignition system related I would put money on the coil pack being at fault. How many miles has the car done? The leads may need replacing as they degrade over time.

 

Thanks for that Phil. The garage was supposed to have changed the leads and the plugs so I don't know
I'm having it dianosed again by a guy who was introduced to me by a mate so we'll see what he comes up with.
Meanwhile the engine light shines bright

 

As said you can try and get it off the old unit, normally the problem is they get gunked up, you can remove and GENTLY clean the wires as they are very delictate, and see if this solves it?

Martin