95 XJ Rough start, stalls when revved

Haven't posted here in quite a while, but recently ran into a problem with my father-in-law's '95 XJ (4.0L, AW4, 170k miles), it starts EXTREMELY rough. It takes 3-4 tries to get it started, sometimes it just stalls, when it does run it sounds like it's missing for 10-20 seconds before smoothing out, but the idle is high (1000-1100 rpm). If you attempt to rev the motor at all, it sputters and all kinds of black smoke pours out of the exhaust (smells like gas). I'm not sure if this is a combustion problem, sensor problem, or maybe a bad injector.. Hoping maybe someone with more expertise with these problems can help me narrow it down.

The exhaust manifold is only about 6 months old. Recently replaced the O2 sensor, fuel pressure regulator, throttle position sensor and fuel filter. I did unplug and plug back in the MAP sensor.

Any help would be greatly appreciated!

Thanks,
Jeff

Just pulled the CEL codes (forgot I could do it, too used to my own '89), and I pulled a 12, 22, 51, and 55. The only one that has me worried is 51 (Oxygen sensor stuck at lean position), but the o2 sensor is brand new.

The high idle may be indicative of a vacuum leak. Have you done a check for vacuum leaks yet? Does it idle high just at startup or does the high idle remain when engine is warm?

Does it start hard only when cold, only when hot, or all the time? Knowing this may be helpful.

With multiple codes, I always start by focusing on the lower number codes first. The 12 is not a concern I don't think as it deals with memory being cleared, but the 22 is a coolant temperature sensor code. I would start there as the CTS provides very important data to the computer about engine temperature and the computer uses that input to help determine how much fuel the engine needs. The CTS can be checked for resistance; not too expensive to replace.

12 indicates begin codes, 55 indicates end codes, so all you are reading is 22 and 51

I had an error 22 the other day after swapping my thermostat. The XJ will NOT run if the coolant sensor is bad. Replace the sensor ($25.00).