97 Deville with multiple codes & hard to start

[mfh11]

Greetings all. I'm trying to help a friend that is having problems with his 97 Deville. He tells me it is very hard to start in the morning, has to crank it about 30-45 seconds before it turns over, gas mileage is very poor, runs rough and sometimes makes a small popping sound for a short time. Running a scanner has come up with multiple codes: P0131, P0151, P0171, P0137 and P0300.
Could somebody let me know what the codes are and if anyone has any suggestions it would be greatly appreciated.

Thank you for any help.

[maxwedge]

Shows lean fuel trims. could be a bad plug. wire coil, also check fuel pressure, bad o2 sensors can aggravate all this, this needs a fuel scan a diagnostic check to point the problems, no quick answer.

[DFBonnett]

http://www.troublecodes.net/OBD2/Pcodes.shtml#300