I've been having trouble with my RS1800 for a while and it's been suggested that it could be the MAF sensor. Yesterday I decided to swap the RS1800 MAF sensor for a 1.6 Si MAF sensor (they're not the same), it didn't really make a difference so I put the RS1800 one back on, the car is now worse than ever. Was this a really bad idea?

When I put the RS1800 sensor back on, the car kept revving itself up, going between 500 and 2000 revs, when I drove the car it kep mis-firing, lurching and eventually cut out. The only way it will run now is when the accelerator is being depressed. It's also a lot louder than before and sounds awful.

What could have happened?

Any ideas or advice appreciated.

Thanks