Slight Surging when holding consistant speeds

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yourrealdad

New member
I just bought a 2006 V8 w/ 126k. I don't know how to describe it, but it almost feels like the transmission is downshifting, or the brakes are quickly and gently tapped, or getting hit with a blast of headwind.

That being said I notice no difference in speed according to speedometer and maybe, maybe a slight dip in rpms, but nothing huge probably not even 200 rpms, I can't really tell.

If I am on a bumpy road or accelerating I can't tell if it is happening it is so slight. I have to be on a smooth road and holding a steady speed (not using cruise control). It is most noticeable on the highway from 60-75mph, but happens around 30mph as well, I think.

No one else in the car can notice it, including me when I had my dad drive it. He didn't notice until I told him what to look for. It doesn't sound like engine braking to me because I have my foot on the gas slightly and on a flat road.

Idle is fine and acceleration is fine. Shifting is super smooth and I barely notice it actually shifting since the tranny flush. Nothing feels rough as far as that goes.

This was happening before all of the following maintenance was done and is still happening.

-Timing Belt and Water pump, belts, etc
-Wheel balancing and alignment
-Full brake flush
-Full transmission flush (shade tree version)
-Differentials and T-case oil drain and filled
-MAF cleaned
-Throttle Body cleaned
-Cabin air filter changed (I figure has nothing to do with it, but it is done)

I have ordered spark plugs and a new PCV valve and will put them in this week.

Any ideas what is happening? Can VVT cause this?

Thanks again.
 
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Turn AC control off. Does it go away? I've found that at a steady pedal I can feel the compressor kicking on/off and it causes a noticeable acceleration/deceleration in with my butt accelerometer but road speed stays fairly constant.
 
The Grand Wazoo said:
caliper or wheel bearing? :noidea:

do you have a noise that feels/sounds like cupped/loud tires humming?
Click to expand...

Could be caliper, but my mechanic when I had it checked out said brakes looked good. Would a stuck caliper cause this?

Bearings seem good and no noise or leaking fluid.

Tires were just balanced and while not perfect do not make noise.

I will try the AC today, because I had it off this morning and I don't think it was doing it, but it was also windy so...
 
It could be a loose suspension or steering component giving you a very slight wandering sensation that has nothing to do with the driveline. Did your mechanic check the shocks, ball joints, control arm bushings, tie rods, and/or rack bushings?

I'm not saying that it has to be one of these things, but it is more likely than your vehicle speeding up and/or slowing down on it's own. That is if the A/C compressor isn't the issue. That would make a lot of sense.
 
Based on your description, I would say it is AC; like you said it very slight and most of people (probably 99% of drivers) will not feel it (including my wife.. LOL):lmao: but some of us are very “sensitive” and we can feel it… I know I can feel it on my truck…

I do not feel it at all if I am towing anything (even empty small trailer) or pushing the truck a little harder than 60-70 miles an hour cruising- so basically anytime any small extra power (vs. maintaining steady speed without any load\wind\incline etc.) is required from the engine)
Also, cruise control is fast enough to react and removes the “surging” of AC cycle so you not going to feel with cruise control “on”

To add more details on that: The reason you feel “sensation of braking” is because it is happening when AC actualy cycles “off” not “on”... Probably because ECU drops too much of power when it knows that AC has been cycled off- I am sure it is related to fuel saving approach and Toyota did not do very good job on that… at least for a very “sensitive” drivers... it is totally opposite to most of cars when you feel slight loss of power (drag \braking) when AC cycles “on” and “rubs” the engine power…

You can play with AC (by manually turning it “on” and “off” to verify…) and again you will feel that “slight braking” when you turn AC “off” not “on”.
 
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Awesome, thanks for all the feedback. It was super windy again here today and hot (probably not as hot as Fort Worth) so I didn't get to test the AC theory as well as I wanted, but I am leaning and hoping towards that.

I will keep testing it this week and report what I find.

Thanks again because I never would have thought of AC.
 
I have been having the same issue on my 04 for a while now. Its the exact same feeling that you are describing. It doesn't happen when the AC is off but since I'm in Florida the AC never goes off in the summer.

Any ideas on how to fix this or make it go away or is it something we just have to deal with?
progress4m said:
Based on your description, I would say it is AC; like you said it very slight and most of people (probably 99% of drivers) will not feel it (including my wife.. LOL):lmao: but some of us are very “sensitive” and we can feel it… I know I can feel it on my truck…

I do not feel it at all if I am towing anything (even empty small trailer) or pushing the truck a little harder than 60-70 miles an hour cruising- so basically anytime any small extra power (vs. maintaining steady speed without any load\wind\incline etc.) is required from the engine)
Also, cruise control is fast enough to react and removes the “surging” of AC cycle so you not going to feel with cruise control “on”

To add more details on that: The reason you feel “sensation of braking” is because it is happening when AC actualy cycles “off” not “on”... Probably because ECU drops too much of power when it knows that AC has been cycled off- I am sure it is related to fuel saving approach and Toyota did not do very good job on that… at least for a very “sensitive” drivers... it is totally opposite to most of cars when you feel slight loss of power (drag \braking) when AC cycles “on” and “rubs” the engine power…

You can play with AC (by manually turning it “on” and “off” to verify…) and again you will feel that “slight braking” when you turn AC “off” not “on”.
Click to expand...
 
I have the exact same thing happening. I determined it is from the AC being on and turning off. Should be the same for you.
 
I have a 2005 4Runner w/v8, and I notice an initial "bump" sound as the a/c clutch engages, but no other sensations or lack of power appear with normal driving and use of a/c.

Not that this would relate to your Toyota, but I previously had an Expedition that was AWD and suffered from these exact symptoms after replacing the two front tires. The difference in tire diameter between my two new ones and the old ones caused the computer to pick up this sensitivity, and it acted just like you're describing. Buying two more tires immediately cured the problem. Again, not sure the vehicles can compare with different but similar drive trains, but it would be an easy thing to dismiss if you can quickly inspect your tires for consistent wear, pressure, and size.

Hope you get this figured out...this is a great place for knowledge and help! My go-to for anything!
 
SluiceboxSlim said:
I have a 2005 4Runner w/v8, and I notice an initial "bump" sound as the a/c clutch engages, but no other sensations or lack of power appear with normal driving and use of a/c.

Not that this would relate to your Toyota, but I previously had an Expedition that was AWD and suffered from these exact symptoms after replacing the two front tires. The difference in tire diameter between my two new ones and the old ones caused the computer to pick up this sensitivity, and it acted just like you're describing. Buying two more tires immediately cured the problem. Again, not sure the vehicles can compare with different but similar drive trains, but it would be an easy thing to dismiss if you can quickly inspect your tires for consistent wear, pressure, and size.

Hope you get this figured out...this is a great place for knowledge and help! My go-to for anything!
Click to expand...

It has brand spanking new rims and 4 new tires.

homasroveo said:
It could be a loose suspension or steering component giving you a very slight wandering sensation
8ce1.jpg
Click to expand...

When you say "loose" do you mean nuts and bolts are loose, or bushings are worn, or say play in the steering?
 
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