Volvo Repair: Mysterious starting problem, air intake hose, fuel pressure regulator

Question
"'87 740 GLE starts 100% of the time if the air intake hose to the manafold is disconnected and a shot of Carb cleaner, WD-40, or maybe shaving lotion is sprayed into the TB. This always results in an instant start but rough run until warmed up and then it smoths out. However if this step is skipped I can crank the car forever and nothing happens. Previously the car would start normally about 1 in 50 times but it is so consistant to have to spray the carb cleaner that I no longer try to start it without doing this. Not always pleasant in Buffalo winters.
Both fuel pumps and fuel pressure is good. Injectors work perfect. Spark is present. Jetronic unit works perfect as well as air sensor (swaped with known working units-no change). Same with fuel relay. Fuses all good and troubleshot.
Hall efect sensor is good. Check valve replaced. FPR replaced.
I suspect I can not be the only person on earth with this experience and would appreicate any input from anyone who has experienced this situation or anyone who might have any suggestions to fix the problem. 4 different garages have not been able to do so. Of course, I suspect a dealer could at $$$$$.
Thanks in advance.


Answer
I would check the the spark is blue in color and strong not yellow or orange looking which would indicate weak spark.weak spark could do this.also be sure there is no fuel leaking out the vacuum side of the fuel pressure regulator I have seen this cause long cranking but not a no start.I will check around to see if others have seen similar problem and see if I can find any other possibilities.