Last week I replaced my air filter since the previous owner had no record of the last time it was replaced. (I purchased the car in Nov.) When I pulled the old one out I was not surprised to see that it was nasty.

Unfortunately, now when I start the car cold, it starts readily but soon settles into an awful idle. It idles very rough, no great fluctuation in revs, just rough. Applying throttle results in slight hesitation followed by more rough running at increased RPM. This endures until the car gets close to normal operating temperature at which point it settles down and runs like a champ.

Since I haven't worked on fuel injected engines I'm not too sure how they deal with cold starts. I'm hoping for some insight and suggestions about what can be adjusted or checked to solve this problem. I hope this is related to my new air filter and not just some evil coincidence.

thanks