4Runner Vibration

2003 4-Runner, SR5, V8, 4x4. Perfect vehicle since purchased new. 86,000 miles. Tow boat (2500#) just during summer months. During recent oil change, shop recommended replacing the serpentine belt. Immediately after the work, noticed a driveline vibration. It occurs when in overdrive, slight grade uphill with a very light throttle; 35-50 mph. The vibration is from the driveline. If you get off the throttle, vibration stops immediately. Same if you step on the throttle and increase the RPMs. Over the past three months, it has gotten better but still occurs once in a while. Independent shop could not duplicate problem. Took it to Toyota and they had the vehicle for the better part of the day. Head mechanic was stumped and the only thought he had was a misfire. No diagnostic codes but suggested replacing all platinum plugs. Followed his suggestion and problem remains. He is stumped and has no other ideas. My belief the vibration is tied to the serpentine belt replacement. Shop told me it is auto-tensioning so they cannot make any adjustments.

Truck drives great and is the best made vehicle we have every owned. We plan to keep it and run it into the ground. Need some advice…

We have a 2003 4Runner, but ours has the V-6 engine. We had considerable problems with the serpentine belt squeaking just after we got the vehicle (brand new). After the belt was replaced three times and the squeaking persisted, the engine started leaking oil. The belt had not been installed correctly and it pulled out the oil seal. I finally asked the dealership to either buy the car back or fix the problem. It turned out to be a bad belt tensioner. In your case, I wonder if the belt tensioner allows the serpentine belt to vibrate in certain engine rpm ranges.

I really like the 4Runner and have had no problems since the initial troubles with the serpentine belt and tensioner. It has also never seen the inside of a Toyota dealership since that point. I have all the servicing done by my independent shop.

What you have described is what happens as U joints slowly deteriorate. The rollers in the bearings will find a position and cause a vibration, then move to a different position and not vibrate. Over time, the vibration will become worse and worse as the rollers in the bearing break adn allow more movement - until the joint fails completely.

Thank you for both replies. This gives me something to go on. I will investigate both sugguestions.