Valves and Valve Springs

[bp2ooo]

My 240 is running like crap. Doh, im not quite sure what is wrong with it. First of all it has a really rough idle, it goes down to around 500 at times, and likes to die occasionally. I think it could be the Maf, but i tried cleaning it and still didn't help. Might be the O2 sensors, but if i keep just trying to guess i will spend alot more money then i have to, so im wondering if anyone has any ideas, or seen similar problems, The rough idle makes my car always sound like its camed, and wants to die... Other then that my valves pop very loud around 3000 rpm, and up. When i stay below 3000 they are quite. I called a nissan dealer ship, and they said they were non adjustable, but it might be a broken valve srping? Does anyone know what valves, and valves springs will cost me, and if there are any performace aftermarket ones, or am i gonna get rapped at the dealership. Please let me know any and all idea's. Thank you. Chris

95 240sx- 13.9 @ 10291 Acura Intergra- Dailey driver

[MasterMan]

rotor and distrubitor cap.. thats what was wrong when mine did that...