I'm having a similar problem with my 93 SC400. It tries to start and sounds like it should but its just not firing all the time. I've found that if I try starting it in short bursts it will catch as well as letting off the ignition quickly. When it does fire, it seems like it idles low and rough for the first second or so and then runs fine. This is a recent purchase and I have next to no knowledge on the workings of this car or where things are located. I took it to a Toyota dealership for a diagnostics test but they couldn't pinpoint the problem either. They suggested the fuel filter or possibly the crank position sensor but I have no idea. Any advice for where to start would be much apreciated!!
