my 91 loyale is running rough

 

also my check engine keeps coming on about 2 min after driving

 

then every time i start it its not on only after 2 min of driving

 

also i have a plug in the # 4 of the block that is bigger than the

 

rest of the spark plugs like someone broke one before and

 

retapped it so you have to use a bigger plug i dont know if

 

this could mean anything but i thought i would mention it.

 

also when i am at idle my oil pressure is almost 0 but when i am driving it . the pressure goes to 40 is this normal on a 5 speed manual transmissions.and could it have anything to do with rough idle or check engine light coming on after 2 min of driving.

Get the codes from the ECU using the guide here and report back. That'll give us a start to diagnose what's going on.

 

http://www.ultimatesubaru.org/forum/article.php?a=44

 

The stock oil pressure gauge isn't that accurate. I think that if you're having major oil pressure problems, you'll hear the lifters start ticking like crazy, and other noises from under the hood.