Mk2 GTI engine issues

[CDubbz]

I own a 92 MK2 GTI. I have been having a problem with it running normal. Symptoms are
- really bad smell out the exhaust
- blows smoke at an idle and when i get going
-idles can either rev to high or to low, and sometimes surges up and down
- misfire like a burp while driving.
-looses power, tach drops then kick back in with a big back fire.
-Sometime it won't start again for up to 15 mins.
-if i turn the key off then back on it usually changes its issues when it is having issues. Except when is quits completely.
-Its even at times it feels like its firing order is all messed up. Like its firing early then i pull over and and it smartens up after a few mins.
Some days it can be worse than other.
Things i have looked at are replaced....

-O2 sensor, plugs wires, cap,rotor, fuel injector o-rings.

If you have any ideas that could help me find the problem i would like to hear from you.

[CDubbz]

When its not acting up it runs great except for the smell really intense out the pipe. Its something thats shutting down the system. Tonight i took a look at it and it cut out for a good 10 mins. On first start it fired and died right away. Each time i cycled the key the fuel pumps would kick in. The tach jumps about 1000rmp for a sec then back down. Car does not fire.
With the key in the On position i took a look under the hood. This is the first time i witnessed this...The injectors, fuel pump and the idle stablizer plunger was turning on and off rapidly till i turn the key off then back on. Almost like there was a bad connection to the computer.
Also sometimes when im turning it over its not giving the starter a strong 12v. Then when i try again its fine.