I have a 90 Toyota pickup that has been sitting up for a couple years. Headgasket blew and head warped. Just recently had the thing fixed and boy does it drive bad.i was told to put seafoam in it and it would clear up but so far no such luck. It struggles to start and when it starts it struggles to idle. When I give it gas it starts trying to backfire in the cold air intake, starts popping and puffing. Once I get through that and give it more gas it'll even out but I have ti apply a lot of gas to get it moving. Once I get past 3rd on the highway it evens out and in able to maintain highway speeds no problem(puffs smoke the hole time near about and smells terrible though) but as soon as i slow down again back to acting up.. Should I just keep running it or take it back? I was told it could be the timing or injectors clogged but wanted some other insight.. Thank you kindly!

 

Valve lash too tight??

 

Explosions in the intake ( back fire ), if I'd paid someone to do head work and a gasket job and they gave me back a vehicle like you described and suggested running seafoam. I'd be pretty pissed, they would be more likely to get sued than get my vehicle back.

Check your valve lash and cam timing, even if you have to buy tools you're looking at maybe $50, the lash is something you can handle in a random parking lot but if the cam timing is wrong your mechanic needs to make it right on his dime.

 

I concur on valve clearance and valve timing. Also check ignition timing. None of these are hard. You can check all three in under an hour if you've done it before.