I have a 99 Cabrio with an intermittent start

Hi, there are a few possible faults that i can think of: the first could be that the battery may be low and does not crank the motor. The second could be that the starter needs attention.(you do not say whether any ignition lights come on) When the key is turned and the motor does not crank, the ignition,battery or the starter could be faulty. I would suggest you start with the battery then test the starter, if the battery is good and the starter is okay then check the ignition. All the best.

The coils in these cars are very susceptible to moisture causing poor engine running conditions, misfires and no start. They also tend to crack. This can be verified with a spray bottle full of water. Simply spray the coil, and ignition wires once you've gotten the engine running if it stalls, arks, misfires idle changes... Replaced the coil and/or ignition wires. Good luck.

check the voltage regulator

You need to the BCM (body control module) scanned, it may be defective.

On your vehicle it has a power stage that what makes it look weak, you may be dealing with a failing ignition coil

There may be no check engine light but that doesn't mean there isn't a code in the ECU. Especially with a misfire. I'd have the codes scanned and see what you got. The cannister issue isn't going to give you a misfire it will give you stalling and rough idle.
Lets see what ECU is saying. You can go to Autozone if you don't have a scanner they will scan it for free. If scanning turns out negative than have a cylinder leakage test done. This way we can determine which cylinder has the problem and what the problem is.

quick fix ,put some card in front of the rad .

My first guess would be a bad idle air control valve if an inspection shows nothing apparent.

I have a 99 vw cabrio and it was doing the same thing. It would just stop in the middle of the street. It ended up being a sensor. I am not very car smart so I can not tell you which one it was. I will look at my repair paperwork and get back to you. I hope that this narrows it down for you though. I also changed almost every part on my car that deals with it starting. It ended up costing me about $1000.00 in the end.

I had the exact problem with my wifes 99 Cabrio - parked for 9 months. Ended up having to have the shop reprogram the ECU - it then worked fine.