My 98 Dodge Avenger ES is using a lot more fuel than usual, is hard to start and get to idle?

98 Dodge Avenger ES 6 cyl. with 150,000 miles...About a month or so ago, hubby did some normal maintenance on my car by changing plugs, wires, changed fluids, ran injection cleaner, etc. and my car has not been right since! The check engine light has not come on, but every time I start it, the starter takes longer than normal to engage, and it is really hard to get it to idle for about a minute...sometimes longer. I smell gas from the exhaust which more times than not is black, then when it will stay running it tries to die when i put it in reverse then again when I put it in drive.... but after that it runs good.....until i turn the key off again! We have changed the TPS, the cap and rotor, fuel filter,and the starter, (because it went out also!) Cant get it to throw a code! Any ideas?