Unexplainable problem-1990 Nissan 240 SX-mechanic is going crazy

[piapetpower]

I just got a 1990 nissan 240 sx. The last owner (my brother) told me that the speedometer goes crazy at times. At first the speedometer would shoot over to the right hand side than to zero, flicker up and down than return to the mileage the car was going. Than one day while driving up hill on the freeway the car just shut down. (or what seemed like it) a few seconds later it comes right back on. As it kept doing this we come to realize that this would only happen up hill, when the speedomter is all the way over to the right, and the rpm are around 3.5 in either 4th or 5th gear. This does not happen all the time or if the speedometer is all the way to the left . Just lately the car won't start. It turns over but acts like it's out of gas. A hour or two later no problem, starts right up. Again this does not always happen. The other on and off thing it does is at a stop you go to take off and the car drops it's idle as you apply the gas. Wanting very much to die. My boyfriend a mechanic of 20 years thinks it might be the speed sensor or maybe the computer. But is puzzled by the fact the car will run good for a period of time than out of the blue it give us one or a set of these problems. Just to turn around again and run good. This is driving me crazy and in return is driving my boyfriend crazy. PLEASE HELP!
Modified by piapetpower at 12:01 PM 6/26/2005

[piapetpower]

Modified by piapetpower at 8:09 PM 6/26/2005

[mega8man]

i had a problem like that with my altima it was the distributer and i had to have the whole thing replaced for one sensor also the fuel filter could be dirty or it could be a fuel injector thats what i was told when mine was like that

[NISTECH]

I think your speed sensor in the speedo head is the speedometer problem. but the no start i think is an entirly differnet issue. You need to determine what you dont have when it wont start, Spark ,Fuel or compression likely not the third.