When I start the car it idles hard and then goes.

When I start the car it idles hard and then goes normal, it does this several times and then idles normal but when I start to drive it seems like it isn't getting gas, it's hard to discribe, then it drives normal. My gas milage has also become very poor. I get 50 to 100 less miles to each tank. I recently had new tires put on a tuneup, new fuel filter and all new fuel injectors. Could it be the oxygen sensors or a leaky air control valve. I don't want to go to my machanic without some knowledge of the problem. Being a woman, it is easy to be taken advantage of. I really need it fixed as my expense for gas has been greatly increased in the past month. This car has run perfect for me for 20+ years (I bought it brand new off the lot in 92) and now it performs poorly for the first time ever. Andi Richards