Engine Performance problem
1987 Plymouth Fury V8 Two Wheel Drive Automatic 197770 miles

I HAVE a 1987 Gran Fury plymouth. i first got her 3 months ago i just changed the oil thats it. i didnt pass my emissions test (the lower end 15MPH test) but i passed my 25MPH test. it this would help,

My problem is at 0TO 18MPH. At WOT she hessitates then acks if there will be an back fire but she dose then serge at 20MPh( she jumps at 20 like shes launching at 0. When shes cold she high idles then smoothes out at ill say 700 RMPS.

lately after shes high idling she will idle and sound like shes below 700 rpms and she feels like shes going to cut out. after work to day i put her in rev, and she cut off. this is the first time this has happend.

i havent change the plugs, wires coil ext. everythings looks brand new. i dont know about the plugs.

i was thinking she needs to be timed. ive heard nocking when shes cold that gose away after shes warm.
please help dont want to spend money in the wrong area
thanks