bucking at low rpm

[spork]

I have a 1999 Expedition with about 120k miles. It has started bucking at low rpms... For example, if you are doing 50 in OD and begin up a hill, there is something anywhere from a slight stutter to bucking like the 25 cent horse in front of WalMart. If you kick the accelerator and downshift, the engine smooths out fine.

When it started a few weeks back, this was the only symptom. Now there is also an occasional shudder at idle.

Plugs were changed at around 105k.
No check engine light. No codes.

I've had this happen once before and it was a COP, which was replaced... that time it took about a week to go from the onset to throwing a code. This time, I've waited several weeks and still no code.

Any ideas? Ideas on getting it to throw a code?

 

[djewing]

i had a similar problem that i first noticed while towing. bucked a little, slipped out of gear or downshifted suddenly. But not at idle-maybe not related to the other?
Mine turned out to be the shift position sensor on the transmission. Mine is a 2001, 4x4, 4.6.

 

[98EXPY 5-0]

My 5.4L would buck like hell at low RPMs in 3rd and 4th (OD) gears. I had to turn OD off and drive around in 2nd gear most of the time. I thought it was the Torque Convertor, but someone told me that it might be the Coil packs. I changed 7 of the coils and plugs (damn number 3) and it went away.

 

[homer169]

Number 4 is a common pack to go bad because of the cowl water drainage. The number 5 pack is a common one to go back because the egr tube goes past it and causes it to burn. I would have the computer checked if you have a cel and go from there. Thats exactly what I had going on and I had to replace number 5.

 

[nvycrmn]

sounds like you need new plugs and coil packs. when was the last time you had a tune up?