It sounds like the fuel pressure regulator diaphram has a hole in it. Remove the 4 nuts holding the engine cover on. Remove it. You will see,as you look at the engine from the front, the plen. injectors. On the rearward side of the plen. you will see alittle vac hose going into a round almost black and goldish round object that sits in the fuel rail. A small silver clip holds it in place. This is the fuel pressure reg. Remove the vac. hose at the top. Look for wettness or the smell of fuel. If you smell or see any, you will need to rreplace this. Pretty easy. As far as the plugs go, the northstar run plat. plugs that generally go 100,000 miles. Sometimes they break down. You will notice this in a misfire. Access to the plugs in back in easy too. The best way is to remove the cross bar. Then remove the spark plug wires from the coil paks making sure you know where they go. If orig. they will be marked. Disconnect and remove the coil paks. 4 10mm bolts- 1 on each side and 2 on the bottom rear. Once you got that out the plug are under the pak. Install in reverse order. If not the fuel reg. then maybe crank position sensors. Are there any troulbe codes?