code 304 could be a bad intake gasket, but changed that , did a tune up, egr valve, o2 sensor and looked at all the hoses.guess what misfired on cyl. 4 was plugged passages between egr tube and intake. cyl. 4 hole not plugged but 1 ,2 3 was. this caused egr valve gasses being dumped into cyl. 4 causing a misfire. took out 1 plug on each end of the intake and cleaned out the tube and the small 1/8" holes connecting into the intake tube. not hard but still a pain.put plugs back in started up and o.m.g. it worked. no misfire. runs great.now i can go for the e test and hope it passes

I bought this car new in 1998, a Nissan Altima GXE. It needs a new engine now! It has 135k miles . I have taken proper care of the car. Almost all of the recommended scheduled maintenance's were done at the dealership. Oil was changed every 3000-3500 miles. I have started noticing oil leaks on the garage floor last year. Gaskets were changed.. Spent 1000 an year ago in attempt to fix the oil leak and other maintenance. But that did not fix the leak. Put a new muffler per dealer advice as they thought a new muffler would fix the leaks. Finally the engine started making noises and it died last week. I have called Nissan per the dealer's advise and requested that they pay for a replacement engine. After a week they called me to say they can do anything to help me. I would not buy a Nissan again