Engine shuts off at operating temp...Help!

I have a 97 Jetta (no mods), 4-cyl 2.0 engine.
After the engine gets to operating temp, it will just shut off and takes almost an hour for me to crank it up again. I took it to the shop and they said that I needed a new ECM and throttle body (they were going to charge $1300). I found the parts used and replaced them. I still have the exact same problem. I've replaced the ECM twice, so I'm pretty sure that the probability of all 3 ECMs having the same problem is too small. Today, after the second ECM replacement, I let the car idle until it reached operating temp and acted fine. I also revved the engine with no problems. I was going to take it for a test drive and as soon as I put it into reverse and started backing up, it died. I have no idea what the problem is and need help. I accidentally posted this as a reply in the 96 forum, sorry. Thanks in advance.

Can you tell if it loses spark or fuel when it dies? First guesses are ECM & Fuel pump relays or the fuel pump itself.

I'm not sure. How would I check to see if I'm losing spark or fuel?

Only old school trick I know for spark plugs is when the car shuts off and won't start again, keep a sparkplug wrench handy and remove the plug. Have a friend turn the key while you watch the plug. If you see the spark you've got spark if not you don't. Just keep in mind the last car I had to do that with was an 85 ford ranger with a carb. I'm gonna say be patient and someone will have a clue.

It doesn't loose spark. Everything there is fine. I tried disconnecting some of the electrical connections and reconnecting them, but that didn't work either. It seems to me that there is an electrical problem because I can rev the engine all day, but when I put it into gear and release the clutch, it dies and I have to wait about a half hour or so to get it started, even though it'll crank.

I just spoke to a friend of mine who thinks it may be a Mass Air Flow sensor or an O2 sensor. Do either of these sound like somthing that would cause these types of problems?

No, it would be very uncommon. What codes were read that led them to say the T/B & ECM were bad? Do you hear the fuel pump humming when you first turn the key to on position (when it won't start)?

No humming, it just cranks, but won't start. I don't know the code that made them say to change those parts. I know that when I took it to AutoZone to get the codes scanned, it read P1240 "Cyl.4-Fuel Inj.Circ. Open Circ.". I don't see how that could shut the engine off only when it gets to operating temp. I unplugged all the connectors that I could find and plugged them back in to see if there was one that didn't have a good connection. The check engine light went off, but after a 15 mile test drive at operating temp, the problem came back and took a half hour to start back up. One of the people who helped me said that it could be the distributor (that's the third time that I've heard this now). What do you think, could that be a problem? I'll post my other error codes as soon as I can find the paperwork that I got from the VW techs. Thanks for any help.

Here's the newest: I got the car to the dealership (after stalling about a half mile away and having to push it up a slight incline almost the whole way). They rechecked it and now they think that it is an engine speed sensor. Does this sound feasable?

It sounds possible, It isn't uncommon for a speed sensor to lose contact once hot & be fine when cold. It would cause the ignition system to shut down if it loses contact.

It sounds possible, It isn't uncommon for a speed sensor to lose contact once hot & be fine when cold. It would cause the ignition system to shut down if it loses contact.
Thank you. I'm going to let them fix it. I'll let ya'll know if it works. Thanks!

I found the problem, it was the engine speed sensor. $140 fixed it (installed). Thanks to anyone who helped.