I am looking for a problem with my wife's car. It runs fine once it has started. sometimes she gets in after the car has been sitting idle, and it won't start. It cranks over properly but doesn't fire.
Every time I look at it it seems fine. I am looking for a list of things I might check that would cause a condition where the engine cranks but doesn't fire - intermittently.

Would trouble codes help with something like this? It starts and runs normally most often, but fails to do that 10 percent of the time, obviously frustrating, difficult to pinpoint. Has anyone ever compiled a list of thing that would cause a no start condition like this?

some of the items that come to mind are fuel pump relay , shorted wire , somewhere. the car runs fine when it runs. It isn't stalling or anything. so I think I need to look for parts that are involved when the car is starting rather than the circuit it is using when running.



some history :
a month or two previous to this it had problems with rough idle and stalling . I went over many things to solve that such as swapping many parts from my 1990 240. I thought I had that problem solved by replacing the oxygen sensor with a generic (4 wire)one recommended by one of the other readers. It made a big improvement but the rough idle condition returned within a week and I took it into my Volvo mechanic and he replaced the oxygen sensor( for volvo 3 wire one), temperature sensor, and finally Central computer. Yes the central computer had caused the engine to idle terribly.. it ran fine for two months after that.