1990 Volvo 760 my 760GLE doesnt start intermittently, pls H

Hello Guys, this is a hard long one so I thank u all before hand and appreciate truly with any advice or help and hint or even prev. Similar problems and solutions. Thanks for being patient too!
As the title says, my 1990 Volvo 760GLE started to form this random situation back in Oct2007 starting off the blue one day when the car was running very badly and rough burning (u could smell gas) and then it finally died on me in the middle of the road and It never started again, as in it would crank but never fired. So I towed the car to the good folks in Volvo dealership (I am not a mechanic and my knowledge is very basic specially with new cars (>1985)) short story they said that" found the fuel pressure regulator diaphragm broken" and replaced that plus spark plugs. I paid 1/8 of the price of the whole damn car (which honestly had been nice and friendly up to this whole issue for me) and left with it. It ran ok for a week and then the problem occurred suddenly again. The car wouldnt start after being driven for a while, crank but not firing. So I towed it back to them and they held the car for a MONTH, doing tests and nothing, at the end they asked me to take it. The verdict was becuz the problem is so random and intermittent and basically it didnt fail on them enough they couldnt fix it. They somehow said that the spark was weak and changed the Coil wire. If u ask me I say I saw my car sitting there for a month and there was so much dust on it that u could tell they didnt really drive it in different conditions so that it would act up. Anyhow, being broke and not able to negotiate I took the car off. It dragged the same way so unreliable I couldnt even drive it for a few blocks fearing if I turn it off it might not trun on. The car would work for a few days, never showing any sign and then one day out of blue just stop starting. I tried to feel it and see if anything happens just before it, all I could figure was it mostly, not always, happened when the car was warm, as in had run a bit before the "start". Also I could tell when it was running it wasnt smooth like a yr ago, the engine would rev up for no reason even when the car was stopped behind light sometimes want to jump off! So I took it to another independant mechanic explaining the whole story. He did some tests, and being a Volvo expert he said its one of 2 things; either the Relay (if I spell right) for the fuel pump or 2 other relays under the hood on the passenger sides or some other thing. So he did his test, the car had sparks and it had fuel! He changed the Relay (green) from the inside under the dashboard on the passenger side, I read myself in the manual that the fuses should be checked (#30 & 31) I did check they are fine. I took the car out, he too said the car was fine and never died on him (?) So I paid for the labor and part and left. 3 days after the problem came back now being stronger in probability of incident. U could bet every other day it would sometime happen if u were driving it. And it did, and drove me crazy. Not having a reliable car and having paid 2 mechanics. So I asked a few people who have had volvo's and they told me that they had sth similar but never the same problem to be exact, I got another name, a chinese mechanic who is not so tactful but is claimed to be best, and doesnt speak much of any english, or at least one I understand (sorry for the story! No disrespect) I say this becuz I dont understand half of his stories, however wut I do understand is this: he tested the car for power (sparks) and Fuel pressure and it always has both. So he has started this elimination process, and he keeps telling me he is going to change part by part unless the problem stops, to me, this is insane! So Far, he has changed first, Speed Sensor, which we have no proof mine was not fine, the car ran for 2 days and boom again it happened same symptoms same results, towed it back to him, he said keep the part he changes another part if the problem comes back he is gonna give me my part and money. (Not the case so far!) So next he changed the Ignition Module last week after testing another thing which I couldnt get for the life of me (something on the driver side to do with air, small 2x2 inch black plastic sitting on the middle of that big pipe thing going to filter, sorry for poor lingo!) The car seems to be fine, It died only once so far, the thing is each time this happen I have learned if I walk away if possible and leave the vehicle and come back next day or in a few hrs there is a good chance to start it again, but this is not the car I would wanna have. U cant really drive it anywhere without thinking if u need a cab or bus ride each time. Very frustrating and unreliable, plus I feel I am being absolutely ripped off by all these mechanics, and the process shouldnt be like this. I dont want to spend more fortune replacing all the part of the bloody car to fix a problem. So here is my plea to you experts, Wut do u think is the problem? If I can put it in my own lame simple terms, I see for the ignition to happen I used to think, know, u need 2 things, which I have both here at all times: Spark, Fuel. Is there anything els needed? Do I need Air, or a rhythm of some sorts, somewhere I read the injectors should shoot in a specific order inside the valves to start the engine, is that true? Wut controls that? Is there any tests or signs u would guide me to pls?
I would take any advice. Open and listening brothers !

once again thanks a 1000 worlds,
Naderxaan