1998 5.7 Vortec P0304 Code?

hammerless-12 · April 26, 2011

Hi all, Im new to the forum but am sure glad I found it.

I am at wits end with this darn truck. I purchased the truck new in 1998, it a GMC Seira 1500 4X4 with the 5.7 Vortec engine. Its been one heck of a good truck and I take really good care of it. Shes got 180,000 miles on her and has run like a new truck up until a couple weeks ago. I had a buddy with me and we went to our local home improvment store, when I was at idle and stopped in the parking stall the engine idled really rough. It was bad enough that it shock the truck and I though it was going to die. when I drove it home she would run fine at anything other than idle, at idle it would run rough and sometime more rough than other times. I didnt want to keep driving it that way so I installed new AC Delco platinum plugs, plug wires, cap and rotor, this may have helped but only slightly. I then got online and found that GM has an updated spider assembly, the one that replaces the old style poppets with the actual injectors. So I got those and put them in one afternoon. I was very carefull and took my time, so as not to damage anything in the replacement process. This seemed to make another slight improvement. I still have a rough idle that kinda comes and goes, if anything it may be a little worse when the engine is cold. At times it is barley noticeable, other times it is real noticeable. The SES light will come on but then go off a day or so later. I havent had the codes checked as of late. The engine uses NO oil and is still really good on fuel. The old plugs looked very good, nice and even, and all very near the same. No knocks or odd engine noices. Still has loads of power and runs like a bandit down the highway. But I know you folks know way more about this stuff than I do.

Some other things I have had done in the last couple years.

(1) New fuel pump (2 years ago)

(2) New intake casket set (5 or 6 years ago)

(3) Two new o2 sensors (last summer)

(4) I did blow out the by pass hose at highway speed and lost all my coolant, so I did replace that hose. The engine did get a little warm, but I knew it went and pulled off to the side and promptly shut the motor down.

I guess thats about it. I sure hope someone can help me, I love this truck and wish to continue driving her. Thank you in advance for any help or suggestions you may have.