Tough question

[don's 4runner]

I own a 1991 4runner 4X4, with the 3.0 and auto. It has a lot of miles (359k)I bought it a little over 2 1/2 years ago, and have just changed the oil, new battery, front brakes and a new radiator in the time I've owned it.. I've only put about 13.5k on it since I bought it. (winter truck) Now my problem, sometimes while drive down the highway (70mph-80mph) the truck seems to lose power and starts shaking some. I can still speed up, but you can feel it's not running right. The rest of the time it fine and goes down the highway smoothly. The shaking has nothing to do with the tires or the road. It's like it starts missing some, does not set off a check engine light and does not happen everytime I drive on the highway. The truck starts up fine, idles fine and I've only had this issue at speeds 65 and up, again not all the time. I'm sorry about the long post, just trying to give as much info as I can. Any ideas will be very helpful. A Big Thanks for any advise! If you need other info, please ask.

 

[Maritimer]

Well, it's a good one, that's for sure. Just want to follow this one, myself.

 

[Crawlin85]

Possibly an out of balance or bent driveline? If it's not balanced it could cause a shake and power wouldn't be directed to the wheels efficiently. Only thing I can think of

 

[jbickers]

I say injector going bad or o2 sensor.

 

[the_dingman]

I say injector going bad or o2 sensor.

I was thinking injector myself.

 

[2Walker5RS]

MAF or TPS is where I would start... I think a bad injector would be more broad across the power band...

You might have a dead spot in the TPS, do a simple OHMS check using the diag port under the hood...

Try cleaning your MAF and throttle body with a appropriate cleaner...

If all elese fails I'd move on to an injector:cheers:

My 2 cents...

 

[don's 4runner]

I say injector going bad or o2 sensor.

I was thinking fuel injector's too, I'm running a bottle of FI cleaner through it and will see if that helps. I'll let you all know. Thanks!!!

 

[Tornadom]

Any chance it is coming from a rotating source such as a drive-shaft, tire or rim?

 

[don's 4runner]

Any chance it is coming from a rotating source such as a drive-shaft, tire or rim?

I don't have any idea about it coming from the drive-shaft. I do know that it's not the tire or rim. After I filled up and put FI cleaner in, I drove 40 miles to work with no issues. I will just have to drive it, till I can figure it out, or until I can make it act up. I'm NOT going to take it to the shop, so they can charge me to drive my truck up and down the highway till it acts up. Maybe I'll get lucky and my FI were just a little dirty.

 

[ChoochCharlie]

Sounds like a fuel issue to me.
Filter? Pump not maintaining pressure and keeping up with speed?
Injectors?

 

[fourwd1]

If it was a driveline or tire balance problem it should happen all the time under the same conditions, not intermittently.

So it's more likely an EFI problem (fuel or spark), like TPS, VAFM, injector, or something simple like a clogged fuel filter.

 

[mcbain]

My 91 SR5 Limited 3VZE does the exact same. It will run fine at 80km/h and at 105-110km/h but it does this shuddering thing between 90-100km'h, but like the OP said, only sometimes. I'm about to change my o2 sensor, and will possible replace the fuel pump. I did the engine light 'diagnostic test' and it names the o2 sensor fuel pump/system.