Not holding RPM's in 4L??

Hi everyone, new Taco owner here.

2018 TRD-Offroad DC in Blazing Blue.

I was testing out the 4L the other day while off roading, I noticed that when in 4L shifted to 1st on a steep downhill, the truck will not hold rpms and would climb in rpm letting the truck roll for a few seconds before dropping back to what it supposed to be and it continued to do that, therefore the truck couldn't normally crawl in 4L 1st gear without crawl control.

I've owned plenty of 4wd's, all Toyota's and none have done this or any other truck in 4L that I've driven, I haven't driven other 3rd gen taco's either to see if they're the same. Toyota had a look today and said everything seems to be normal and they reset the ECU to "re-learn" my driving. I suggested they do a tranny fluid check even the service lady acknowledged that the tranny might be slipping. They didn't do a fluid check and the truck came back as normal from the techs after they took it out for a drive and checked for tranny software updates.

They didn't mention the 4L either if it was normal or not, just told me not to use it on dry pavement. facepalm

Does anyone's Taco does this too or is it normal for these trucks? Any advice is appreciated. Cheers

 

I'm having a hard time understanding what you're describing...you're saying that when you put it in 1st gear in 4lo on a steep downhill, the RPMs climb higher and slow the truck down? That sounds completely normal to me, that's exactly how my 04 behaves.

1st gear in 4lo is very low and even on a steep hill it'll slow itself down to the point of stalling if I allow it to (manual trans). I see that as a good thing as it keeps me from having to ride my brakes on a steep hill.

 

Eon_blue it is actually doing the opposite, it starts off normal in 4L at the proper rpm where it slows and crawls nicely, then after a few seconds the rpms will climb even higher making the truck roll faster before the low gear engages again slowing the truck back down to a crawl.

It will do this back and forth, a few seconds of crawling nicely like it should, and then the rpms will spike and feels like the low gear disengages and the truck starts rolling faster and faster, when the rpms hit around 3K(by this time the truck is super loud) the truck will slow back down start crawling again at the proper rpms. In a slippery or rocky/bumpy situation this could be dangerous because the truck starts rolling pretty good that you got to tap the brakes a few times before it slows down again.

I will try to get a video of this happening as soon as I can.

 

Hmm that does sound not-normal...hard for me to compare though with an older truck since I don't have CC or some of the same features...hopefully someone else will chime in soon though. Welcome to TW!

 

If you have a manual trans, the clutch is slipping. If you have an auto it’s sounds like it’s starving for fluid. Either the trans fluid level is too low or the hill too steep and the fluid is not reaching the pickup tube (or both).

 

If clutch was slipping the speed would go down or not change. Hes speeding up and having to press the brakes (I think). So it's a throttle sensor issue (are these drive by wire?) Or ECU or idle problems.

Is it the terrain speed control acting up?

 

Did you have the air conditioner on? Idle speed fluctuates as the compressor cycles on and off. That is what your description sounds like to me. Perfectly normal if that is the case.

 

What about the surge some get with turning the wheel? If the trans was slipping it would do it in 2wd to. Torque converter maybe

 

Correct

Power steering pump also increases the idle on demand causing fluctuations in RPM.

On manual transmission trucks the brake booster also does this.

 

Ok, before this gets out of hand... I'll relate what I can from a 3rd gen M/T perspective.

This behaviour (at least on a '16 M/T) is normal. As far as I and a bunch of other M/T owners can figure, this has everything to do with decel fuel cutoff.

AC off, steep downhill, 4lo 1st gear and crawling. You're slowing down (not touching the gas), and when the RPM reaches ~1300, the engine braking suddenly becomes noticeably less (injectors on). If you don't hit the brakes and let the truck accelerate to ~2500 rpm, the higher level of engine braking suddenly comes back (injectors off). To test out the theory, I turned the ignition back to accessory while the truck was doing the higher engine braking part of the cycle - and guess what - the engine braking stayed the same. Don't worry, I did it in a safe manner lol - besides, my OR has an electric brake booster and the power steering pump was still turning with the engine.

You can even replicate this cycle (kind of) in neutral by revving the engine. With the AC off, give the truck some gas but don't rev above 2500. When you lift, the rpms fall back at pretty much a constant rate, right back to idle. Now, rev it just past 2500 and watch what happens when you lift - the rpms will fall a bit quicker, then when it reaches ~1300 you'll feel a small jolt, the rpms momentarily stabilize, then they fall to idle.

Also keep in mind that the 2GR-FKS is using the "pseudo-Atkinson" cycle at low load and below a certain RPM (I didn't pull this out of my ass, Mat from OVtune has mentioned it several times). This means lower compression.

Anyway, take it or leave it.

 

Thanks MOC221_ for your reply, I forgot to mention that my truck is the A/T and not the manual. What you described is basically what is happening, the engine breaking definitely became less letting the truck roll before coming back on. I also had the A/C off too.

I will have to take it out to see again after having a Toyota take a look at it and resetting the ECU, not sure if that did anything else but the truck does feel better and a little more responsive now like it did when I first bought it.

 

Its the suck ass gearing they put in these trucks, Mine does the same thing , it keeps gaining speed and the RPMS keep rising and then it catch's itself and surges back down, I am re gearing next week

 

Understood, and I wouldn't worry too much about it. It IS annoying in that situation, that's for sure.

Enjoy your truck and stay the heck off here if you can lol.