Have 1986 chev s-10 pkup. 2.5l 4-cyl, fuel inj 5-speed manual. When I start with engine cold (surrounding temp, any weather or season) there's a solid, dead miss. The further I drive the miss starts to gradually go away. Eventually about a mile, miss is gone. Doesn't return until engine is off, cools down. Never overheats, has gotten worse last several months, taking further to go away. Suggestions? Thanks. Ron