Hi guys I'm new in this Forum. I have been having problems with my truck. I am from México and its too hard to find information or diagrams about it and mechanics are such a liars. Mi truck has a bad idle, runs Fine but in idle rpms go up and down a little like they were jumping, and when I press gas they go up normal and when I stop pressing they go down to 800 and suddenly go up to 1,200~1,300 rpm. I don't know what to do, I've replaced HP fuel pump (truck didn't have it) , in tank pump (because sending unit was bad), fuel pressure regulator, IAC, TPS, MAP, intake manifold gasket, throttle body gasket, and fuel filter. Ignition Module is new too. It seemed like a vacuum leake but my truck just have conected the booster, FP regulator and the MAP to vacuum and I've checked the lines and found no leaks. The missing conections are bypassed with hoses. Also i've sprayed Carb cleaner and found nothing. I hope you can help me because this is driving me crazy.
My truck is a F 150 1987 EFI 4.9 l, straight six and four manual transmittion.
It also reduced gas milleage and gas is very expensive here.
Thanks.