93 F150 4x4 351 Where do I look? shudders between 25 to 35 mph then runs fine. Idles fine shifts (auto) fine cruise control fine replaced tps last week solved hi idle/hard dwn shift Thanks for all help

 

Sounds a lot like torque converter shudder. Lightly tap the brake when the shuddering starts, just enough to unlock the converter. If the shudder goes away, then you know what you are dealing with...torque converter shudder. If it does not go away it could be a fuel problem or ignition.

If it is torque converter shudder the best advice is to do a complete transmission fluid replacement. All 16+ quarts. There is a how-to in the Article section of this site. My last '93 Lightning had this problem. The fluid looked good, a little dark but no bad smell. Did a fluid change, all was good with the world again.

 

Ford dealer did trans fluid about 4000 miles ago and it seemed to shift a little late after they did it. They say they back flush so no filter replace was needed. the back flush pushes fluid back thru filter blowing it clean. I had my doubts about that story and I dont think a back flush is true but who am I? I think it must be n the fuel,, in park if lite press of gas ped it has small vibes/shudder but idles fine.

 

How old are the ignition wires/plugs/cap/rotor? The 5.8L engine is susceptible to cross-fire due to the firing ordering. Make sure the wires are adequately spaced from each other.

 

checked 1 plug looks ok , wires have 20-25,000 miles, new cap/rotor. trk had 68,000 miles when i bought it in 2004 now has 107,000 gets used very little but alot of white smoke out of tailpipe wires are on correct cap studs/post

 

I would suggest to pull all the plugs as well as get some new good quality wires. White smoke all the time? Could be a head gasket...

 

Srry for the time delay but just replaced all plugs and fuel filter. Gas frm filter dirty/black and plugs looked good but were burnt to a gap in excess of .025 fact is .044 they were almost at .065 now runs like a CHAMP idles so smooth hrd to tell it running thanks for all the help

 

Thanks for the feedback! Glad to hear you fixed it.