I have a 1997 Toyota Tacoma XtraCab 4x4 3.4L with a 5 speed manual transmission with 98K miles currently. I just bought this truck 3 weeks ago (I've already put on 3K miles)and fairly new to Tacoma's but am mechanically inclined and been working on cars for 15 years. I have a vibration that is mostly prominent in 2nd gear (initial shift into 2nd so RPM's are 1100-2100) during acceleration but vibration is in all gears/speeds during acceleration. Less vibration when I baby it and lightly apply throttle but can't seem to feel a difference if I press in clutch. No difference in 4WD or 2WD and feels like it's more from the middle of the truck to the front. No excess vibration in gear shift and seems to shift smoothly. I have had the propeller shaft completely rebuilt/balanced (u-joints in CV, rear most u-joint and carrier bearing had play), new OEM NGK spark plugs gapped to .044 and cleaned the throttle body (the ones I took out were very worn OEM plugs and t-body was dirty). I haven't checked the front drive shaft, fluid levels in the t-case, trans or diffs yet. I almost feel the engine is slightly under powered but it runs very smooth at idle and the oil after 3K miles is still clean with minimal consumption and no smoke out of tail pipe. I get 17.5mpg if all 55-60mph driving, 15.5 if all highway at 75mph and 15 average city/75mph highway driving. I don't know if the timing belt was done yet and would be willing to bet it hasn't. The clutch grab is at the top of the pedal but not slipping and the tires are BFG A/T's that have weather cracking in between the tread blocks but not on the side walls and approximately 50-75% tread. Brakes seem good and visual inspection underneath reveals no fluid leaks, anywhere.
The possibilities I have come up with:
1.Front drive shaft u-joints.
2.Clutch throwout bearing/pilot bushing
3.Engine timing is off
6.Fuel pressure/fuel filter issue
I know its a long post but its informative! I'd really appreciate someones help. As you can see, I put on a lot of miles and have minimal time for mechanical repairs so pinpointing this issue minimizes down time and just "throwing parts" at it. Thanks Everyone!!!