2001 VW 1.8T intermittent cranks no start EPC+Check engine smell gass

I have a 2001 VW Passat wagon 1.8T automatic AUG engine that has an intermittent issue.

Every few days it will not start. Cranks but no start. EPC and CHECK ENGINE lights are on and there is a strong smell of gas. At this point it will not start for from several hours to several days. Then it will start again and run fine, again for a few days.

When not starting the VAG scanner only gives a link error. When it is in a period when it will start and run the VAG scanner connects and works but gives no error codes.

I have replaced the crankshaft position sensor (also called the ESS engine speed sensor) and the ECM. I am a pretty skilled 65 year old mechanic and a retired computer tech so I pretty well understand auto mechanics and electronics issues and can follow any help given. But this thing has me stumped. Being intermittent I suspect it may be as simple as a flakey ground in some circuit. Odd troubleshooting steps seem to trigger it to be able to start again. Sometimes if I disconnect and reconnect the ECM it will then start. Sometimes just plugging in the VAG scanner will get it to start.

Any help would be appreciated. Getting about ready to sell the car if I cant resolve the issue but also I don't want to dump the problem on the next owner.

Thanks