my van has lost power, has no acceleration at all past 3/4 throttle point (although the fuel gets dumped). It doesn't upshift or downshift (passing) properly at full throttle. I have replaced the tps. my odbII say multiple mifire sometimes, other times it says misfire on cyl. # 4,7. I also hear a sucking sound coming from engine compartment when accelerating. It also shakes a little at idle. Otherwise everything else is fine. also cleaned the iac

 

Take off the air cleaner housing, open the TB butter fly valves and looks straight down with a flash light. If you see oil down in there, you need to replace the head gasket. It's really not a hard job to do, but it takes time and effort to replace the head gasket.

The other issue is, have you been driving the van around with bad gas for a local station? Maybe the injectors are getting clogged.

Peace!

Stev

 

I'll look down there. as for bad gas, yes last summer got some bad gas, after I ran it out I put in new fuel filter and amoco silver (which I usually use)

 

Sounds like you've got a vacuum leak in there somewhere.

 

5.9 and 5.2 are bad about blowing the lower intake gasket and sucking coolant or oil inside them. replaced many in my time.
U can run the engine and spray carb cleaner or brake cleaner around the intake arear and see if the rpm changes as it sucks in the vapors. and there ya go.