hard to start

I'm looking for some help. I replaced my plugs with Bosch Platinum 4 plus, after a week my check engine light went on. Then soon my car would turn over but not start. I had replaced the ignition cassette two years earlier and thought that maybe it was the issue. I found a working used unit and...

car: 1999 saab 9-3 turbo my car turns over an average of 5-6 times before starting. everytime. sometimes more. but runs fine after its started. why? thanks Gage