Hi- I see that this thread is old but I am replying to it in the hopes that someone will see it. I own an Audi A4 Quattro, 1996. It has been having pretty much the exact same problem that you described your 5000TQ having. Sometimes it won't start but most of the time it will. I don't know nearly as much about cars as you do so I can't run any of my own tests, except to notice that when it does happen, it's usually after the car sits between 1 and 4 hours. It has never had trouble starting after sitting overnight. When the problem occurs, it will crank but won't catch for the first two or three times I try to start it. Then on the third or fourth try it will catch very weakly, as if the car is really laboring to start. It then runs hard for a few minutes and if I let it sit there running it will eventually even out. If I push on the gas pedal the car sounds like it will die. If I leave the gas pedal alone it evens out on its own. Once it's running smoothly, it never stalls out on me. The problem stayed like this until one night about a week ago. Instead of starting on the third or fourth try, it just wasn't starting at all. The car had been sitting for about four hours and it was cranking but just refused to catch. I left it alone overnight and it started the next morning. When it started it sounded like it was very very difficult- but it did start on the first try. I drove a few miles and the check engine light came on (for the first time since the problem started three months ago). I took it to the mechanic and the code said something about an oxygen sensor problem, and the mechanic said he didn't think the two problems were related.... so anyway i left it there with them and they've had it almost a week and the problem has not manifested itself. They say it's a very difficult problem to fix if they don't actually see it happening..... anyway bottom line is that I'm totally frustrated, I've listed the car for sale but I can't sell it to someone knowing it sometimes won't start.. my conscience won't let me. Please help me! There's got to be someone out there who knows what the heck is going on!!

 

the shop sould try to pull the codes several times ... after the no start ... but there are alot of possibilites ... bad ground ... bad cam position sensr ...