cranks but won't start
I have a 97 sentra that twice now has had a problem where it will crank fine, but not start. I have replaced plugs, wires, cap, and rotor. EGR is relatively new. Fuel filter gets changed every 30k. When problem happens I go through the Haynes - all wires getting spark, fuel delivery appears OK, injectors ohm out OK, grounding OK, all vacuum lines appear OK, starting fluid doesn't help, no apperant moisture issues. First time this happened (~4 years ago), had it towed to a shop, and they said car started for them first time they tried it and has been fine until a couple days ago - same problem - Sunday night. Checked everything out as described above Monday night - couldn't find the cause - cranks but won't start. Tried first thing Tuesday morning as a last ditch effort before having it towed to a garage - started first time and has been fine all day! Any ideas? It has been cold out (20-30 deg F) both times.
Thanks, any help much appreciated,