Need some help on this one

[4Runner4TW]

Not sure what to make of this phenomenon happening or even where to start diagnosing the cause. Bare with me as I try to explain what's happening.

Cruising at 40-50 mph, down hill or slide grade down, not on the gas pedal or brake, the RPMs will drop about 1000 to 12-1500 then bounce back up. Only way I can recreate that is when you hit the brake and the RPMs drop and rebound. The part that is concerning is when the RPMs drop the truck lags or pulls like it slowing or engine breaking.

In summary the RPMs drop, truck pulls/slows and then they rebound. This all happeneds in about 1 second. Not sure if it's fuel, spark, vacuum, engine, or transmission related..

 

[SilverRidgeRunner1]

Sounds like Transmission may downshifting to me. Video would be lovely

 

[ThorInc]

Could also be your TPS sensor.

 

[4Runner4TW]

Sounds like Transmission may downshifting to me. Video would be lovely

I was thinking that too, but wouldn't that cause an increase in RPMs? The slowing sensation does feel like transmission, but could be from loss of power.

I'll get a video today and post it late tonight when I get home

 

[4Runner4TW]

Could also be your TPS sensor.

In my endless Google search for an answer this came about a lot and was a common issue in all three Japanese brands. Thanks!