1990 240sx won't start

[ry_goody]

So this morning, I drove it to school (about 30 minute drive), it drove just fine except the usuall minor problems such as slightly sparratic idling. On the way back from school however, towards the end of the drive it started to idle extremly bad. It would jump back and forth between 100-200 and 300-400 rpm very quickly, shaking the car rather badly. However, I let it go on like this for about a minute and it never did die completely. So I then took it for about 1 more 5 minute test drive, come back, park and it will not start at all.

The engine turns over, it has a brand new battery, even tried jumping it just in case with no luck.

It's like the entire ignition system is working just fine, but something has come loose and is just not igniting the fuel. I can smell gas, sorta like it is flooding, when I try to start it, so I assume it is getting gas to the cylinders. Which leads me to believe it's something electrical dealing with the spark plugs.

I am fairly sure it is just some sort of plug that has come loose because it went from OK to not working at all in about 20 minutes of driving. But I have pretty much no experience as a mechanic and do not know where to look to see if something has come loose. I am very quick with machinery and mechanical things. So could someone who has had this or a similiar problem could offer a fairly detailed explanation on where to look for any connection problems or something related? Possibly pictures? Thanks in advance for any help, I really want to start being able to fix my own car.

[NISTECH]

try to restart it but hold your foot on the floor and crank the hell out of it. If it fires you are having an extream rich condition going on [ to much fuel being dumped] In that case you want to check your coolant temp sensor connection. 2 wire connector at the front of the intake manifold where the radiator hose goes in. It is usually a red or yellow connector. If the connection is not corroded [filled with green crust] which you would need to clean. Then you need to get a fuel pressure tester and do a leak down check on your injectors. you hook this tester in between the fuel filter and the hose attached to the filter [on the top side] turn the key to the on poition. fuel pressure should climb to between 35 to40 psi. then within 5 sec the fuel pump would shut off or you can turn your key off and that reading should not drop more then 10 pounds. If it does drop you need to pinch off the return fuel line [ the one next to the filter that goes back to the tank] and redo the test. If it still drops now you need to do the test one more time but this time you will be pinching off the fuel line under the filter immediatly after cycling the key [have some one cycle the key as soon as the pressure hits its highest point pinch the hose] If the pressure still drops you have isolated the fuel pressure loss to your injectors. If this is the case you will need to replace and/or reseal your injectors.