Volkswagen: 99GTIVR6, cat converter, cam sensor

Question
Hello, thank you for taking my question. @ 1 month ago, my VW was starting intermittently. While I was stopped at a light one day, the idle dropped very low, I thought it stalled out...but when I pressed on the gas...then it stalled.  My husband changed the plugs, wires, and fuel filter.  No change.  I brought it to a shop and the diagnostic eval revealed the need for: coil pack, temp sensor, speed sensor, cam sensor...and cat converter.  My husband plugged away at everything above except the cat converter.  It started and ran fine for the day.  The next morning it wouldn't start again.  I turned it over 2-3 times..but it smelled like gas so I stopped, he put the battery charger on it and it started.  Then no problem throughout the day.  Then 2-3 days later..the same thing.  It was suggested that before we replaced the cat converter to give the car a week or so to see if the check engine light went out..and let the computer digest the new parts.  Anyway, throughout last week...some mornings it started..some it didn't.  Thursday night it rained...Friday morning tried to start the car...nothing.  It would not start at all...all day.  That night before bed I tried it again...this time I pressed the gas and tried to crank it over 2-3 times.  Then I figured I flooded it out because I smelled gas..so I left it until this morning.  This morning, at 7AM before I cranked it over..my husband put the battery charger on it in fear that I wore down the battery yesterday trying to turn it throughout the day.  He waited about 1/2hr then as soon as he turned the key...the "intake manifold-upper section" exploded!  Yup-EXPLODED!  Then it smoked up quite a bit...but no fire.  The plastic pieces flew over 50'.  Now I'm not sure what to do.  And am even more curious of what happened.  My husband feels that this should of never happened.  What are your thoughts about what happened?  What would you do now?

Answer
Hello there... first BIG question here is..how many miles on this GTI?  You say the intake manifold exploded... but I don't believe the vr6 had a upper intake made of plastic until later years... so if you will...  explain to me what parts actually blew apart on you.  Lets say if you were to start at the plastic 'box" that houses the air filter... from that part and move up... what parts exploded?  
Regardless... I'm pretty sure your problem is not with ignition timing,...but with mechanical timing.  A) if timing is off the cam sensor will throw a code in the computer. (check engine light comes on)  B) If timing is off, the cat. converter will get unburned fuel dumped into it causing excessive heat and bad fuel trim.( check engine light on again)  Speed sensor will probably throw a code because the cam sensor is trying to match engine angle/speed with trans speed and they are not matching.  So my first thought is that your timing chains have stretched, or timing chain guides have worn out and the engine has jumped time.  Normally the first thing that gives this away is a motor that "backfires" through the intake.  Add too much fuel in the intake and that backfire turns into a small explosion.  (Guess how I know?)   hehe    Do me a favor and let me know some of the answers as well as if my info makes some sense to you and your husband.   The expert site is difficult to respond through.... so you can reach me directly to help you along this at :   cmedsaint@yahoo.com

many thanks,
shad