1998 Pontiac Firebird low idle wear noise

Engine Performance problem
1998 Pontiac Firebird V8 Two Wheel Drive 160000 miles

Better description of problem

I have a 98 trans am. 5.7 liter automatic. The problem I am having is it is making weird noise, it idle low(500rpm, it suppose to be around 1000), loss of power, and when at full stop it hesiatate when running again. I started having this problem about a week ago, but the low Idle since I bought the car(about a year ago). At first the idle wasn’t that bad it would shake alittle(low compression because my car would sound quite at a stop light). It only did that in drive, it would not have this problem in reverse nor nueteul. I wanted to fix it so I started fixing thing that would be causing the problem. First I removed throtte body and there was a lot of carbon build up. Nothing, problem remained. Second I changed the Idle air control valve, new MAf sensor, speed sensor. But nothing. Third I gave tune-up, changed oil, sparkplugs(irdium), and wires. When in the process of doing this, I notices oil in the spark plug chamber(a lot). I think that is why I am getting the low Idle. I know that it could be one of 2 things, the pistion rings could be bad or the valve path is leaking oil because of bad seals.(How can I tell?). A month later I stated hearing this noise(bang, bang, like if something is hitting). This only happen in drive, but now even when in park. I just don’t know what to do. I don’t want to take it to a mechanic because where I live(Laredo) no one knows what to do and I also get the run around(like it the fuel filter, Im sure, I put a new one a week after I bought it) any help on this matter, would be great. Oh and it now making a clicking know, I think it’s from a valve.

Mods- egr removed, block off plate.
New headers and y-pipe- slp
New exhaust- flowmasters
Maf-madification
Oil changed – put thicker oil because mechanic told me it would help- 160,000miles, 5w30 to 10w30.
New spark plugs – delco irduim msd wires,
New oil filter –k and n
New air filter – k and n
New temp- 160 degree
New speed sensor
I put some additive in the gas- NOS, etc
Oh and a thrddle body bypass(for coolent)
And also fixed the secondary air system, the smog pump was broken