Heavy vibrating while throttle is depressed over 60mph, but coasting smooth. What gives?

I'm about to move out of state for a 1500 mile drive and want to make sure I'm ready to go! I have a 1998 Base 4cyl 2.7 4runner 2WD. The car runs like a top— I always maintained it well in the last 5 years I owned it. I bought it at 220k miles and its only at 250k now. Funny thing is I never noticed this vibrating so I can't pinpoint when it started, but I drove my brothers 4runner which is identical to mine mostly, and it did not have this issue.

Like the title says, while throttling over 55-60mph, there is a heavy vibrating as if I was going over a rocky dirt road. Upon release, smooth. Still, under 60mph, even on the street, after I release the throttle, there is a light vibration lasting about one second, each time releasing the gas. I'm trying to diagnose this issue, but I haven't gotten any codes or check engine lights.

So far I cleaned the MAF sensor with a cleaning product spray specifically designed for it.
I Replaced the tires with the factory size, since the previous owner had them slightly wider. The tire place checked alignments and weights etc so I doubt it has to do with that. Then checked basic stuff, throttle cable looks fine to me, all fluids at proper levels, synthetic oil always changed yearly, no oil leak or burning. I have noticed when I switch from reverse to drive (always coming to a complete stop first) there is a clinking noise, don't know what that may indicate.

Before I start trying to replace spark plugs etc, I want to see if there was a way to sort of pinpoint wether this is a fuel issue, or transmission, engine mounts, or even just a loose bolt somewhere.

If anyone has any ideas, I would very much appreciate it! Ever since I noticed the vibrating I'm pulling my hair out every time I drive the car! Thanks in advance!

 

Maybe check out the U-joints, and this has nothing to do with your problem, but have you checked your lbj’s? Welcome to the forum.

 

Thanks for the heads up, I'll look into the LBJs after seeing some pics of what can happen!

I'll take a look at the joints tomorrow, is that a common issue for vibrating though? I just don't want to start replacing things before a trip that are in working order, since even though I pretty much can handle most repairs, I'm not a professional mechanic so I tend to err on the side of 'if it aint broke don't fix it.' But I do like to find out if it is indeed broken or not.

If I can't find the issue, I'll probably take it for a full point inspection, but I'm not in the position of racking up a huge bill. Plus I've never had any major OEM part on this car fail or had any overheating/leaking or performance issues (save for the starter, catalytic converter, and heater valve) so I'm pretty confident it's reliable enough to make it. This is basically the first red flag of something potentially wrong with the car that's poking a hole in the confidence armor, and right before a road trip!

Thanks again for the info and the welcome!

 

At 250k i could see a few other things that may need looking at, but that can be another day.

 

A little help, maybe? OK, my recently acquired '00 2x4 4runner v6 auto with 240k miles has developed a new vibration issue. at low speed, under 30, it almost feels like a dead miss, smooths out between 30 and 55 or so, then comes back worse between 55 and up. But anytime its vibrating, if i let off the gas it stops, and its in the seat, not the steering wheel (so no front end suspension/tire prob, I think) and not in the brake pedal (so no brake probs either). No clunk when shifting into drive from park, but a bit of one when shifting from drive to reverse. The check engine light has been on for years (evap cannister, yeah, I know, on my list to get fixed, lol), but when this is happening the ck engine light starts flashing on and off. I helped maintain the vehicle for the last 10 yrs, as in offered advice when probs cropped up, and took to shop for probs when requested. I don't know that rear end lube level ever checked (at least I never specifically told the shop to do it, may have been ck'd as some regular inspection). Getting codes pulled this afternoon. Looking for options, opinions and best guesses. I'm betting drive shaft or rear end.