Which direction should go with this information? on 1997 Cadillac Seville STS

Hello I have a 97 Cadillac Seville that I am trying to get going again. The on board error codes P0300,0108,0603,1599. My code reader picks up P0301. She has to be hit with starting fluid to start cold, hard to start after being warmed up for a few minutes, and won't start until it cools down after it has been driven until it is completely warmed up. If I push down the accelerator past 1/2 quickly the engine almost dies(acts as though starved for fuel) and while idling it will slowly flood until it dies on restart the engine speeds up like it was overloaded with fuel for just a minute or two and then the cycle starts over with the smell of unburned fuel coming out of the exhaust. It will loose power while driving, backfire loudly, and then drive ok for another hour or two.Since purchasing the car it has lost a huge part of it fuel milage 15 to 20%. Any direction or advice would be greatly appreciated Thanks Rich

by in Olympia, WA on October 29, 2013
2 answers 4 comments
ANSWER by on October 29, 2013
Check for restricted exhaust system.
COMMENT by on October 29, 2013
Thank you
COMMENT by on October 29, 2013
Also check map sensor and coolant temp sensor. These two are the most important besides oxgen sensor for governing fuel. Gm cars depend on the coolant temp sensor a lot.
COMMENT by on October 29, 2013
I really appreciate it that helps alot
ANSWER by on October 29, 2013
seek a complete diag on all codes as not to waste time and money,other than misfire on #1 all other codes can be a mulititude of issues
COMMENT by on October 29, 2013
I may end up having to do that now that I can drive it to a shop Can You give me an idea on what that might cost?