90 GM running rough

i recently obtained a 90 MGM with the 5.0 AOD. this thing runs great at anything ABOVE 40mph. under it seems to sputter and run like crap. if i give it a touch more gas it smooths out.

this car ahs a fresh tuneup about 2 months ago, new alt and battery 3 weeks ago, intake and valve covers were done 3 months ago or so. so i dunno what the issue could be. other than needing a good Seafoam treatment and maybe a fuel filter.

so heres my ? to you nice people. the vacuum diagram is gone from this car so i cant find where to do a seafoam treatment other than the brake booster vac line. will that work??? also how hard is it to do a fuel filter on this car? i havent even been under it yet to see where it is but i am hopeing its not in the tank.


thanks guys and\or gals!

Seafoam in the fuel tank and then you can pull the PCV and use a small funnel to SLOWLY pour Seafoam thru that hose. The fuel filter should be under the car near one of the rear wheels - just not sure where it is on a 90. It's near the rear passenger wheel on an '87 and by the rear driver's wheel on an '93.

cool! thanx for the info. i will definatley try to find the PCV valve... as i cant seem to find it right htis second. its buried in there somewhere:D

Check both valve covers. On an '87 it is buried behind the engine just in front of the firewall!!