RPM drop/rebound ? - Page 2 - Toyota 4Runner Forum

HiLife · 02-26-2021, 11:23 PM

Quote:

Originally Posted by cl4Rk

Update: was just able to test. Brake feel is normal.

Try letting the truck sit for a while. Without starting the truck...step on the brakes. You should have vacuum assist on the first push of the brakes and gradual hard on the second push.
You could have a leaking brake booster check valve or leaking booster. Bottom line is booster cannot hold vacuum.

cl4Rk · 02-26-2021, 11:41 PM

Quote:

Originally Posted by HiLife

Try letting the truck sit for a while. Without starting the truck...step on the brakes. You should have vacuum assist on the first push of the brakes and gradual hard on the second push.
You could have a leaking brake booster check valve or leaking booster. Bottom line is booster cannot hold vacuum.

Ok I’ll check it soon and post my findings. Thank you!

19963.4lsr5 · 02-27-2021, 10:49 AM

Pinch off the vacuum line to the brake booster and see what happens.

Sent from my iPhone using Tapatalk

cl4Rk · 12-01-2021, 01:56 PM

Just to update this thread, I have not really noticed this symptom since finishing the frame swap. So I won't be able to get to the root cause unless it starts happening again.

AntonioCm1983 · 02-08-2023, 04:01 PM

Hey everyone Check your Coils you could have a failing coil and the coil is working and as your slowing Down the coil looses power then regains Power and Current spikes on the secondary winding after recovery seen this on Cylinder 1 coil and because it's a waisted spark system 2 cylinders are loosing power momentarily and then recovering to fast for a misfire..... hope it helps all if you need coil ohm specs let me know....

Quote:

Originally Posted by cl4Rk

Over the last week or so, I've noticed something that I can reliably reproduce.

I'm in a 2000 automatic 4wd. I've had the truck for about 2 months now. I don't remember noticing this issue until about a week ago, but it's also possible (likely) I wasn't paying attention to it.

Anyway, with O/D Off, at about 1500 RPMs and 35 MPH, I'll experience a momentary rev drop/rebound when I apply brakes.

Here's the full picture:

Recent work (within last year, previous owner and myself):
- new radiator
- new valve cover gaskets
- new timing belt
- new battery
- new water pump
- new driveshaft
- new cat
- recent oil change
- power steering fluid exchange
- new starter
- new MAF sensor
- new spark plugs
- new coil boots
- new pcv valve
- new fuel filter
- cleaned throttle bottle/IAC
- fixed various vacuum leaks (one that thew a P0171 and another that prevented my 4WD from engaging)

Things that don't seem to matter (this happens either way):
- Coolant temp
- ATF temp
- ECT norm/pwr

Pre-conditions:
- O/D Off
- 3rd gear
- Cruising about 35 mph
- RPMs about 1500

Steps to reproduce:
- Apply brakes to slow down to about 30 mph

Symptom:
- The moment I brake, the engine quickly drops to about 900 RPM before correcting and quickly climbing back up to about 1200 RPM.

Torque converter?
Any thoughts? Something about locking/unlocking/re-locking the torque converter? since i'm in O/D Off, then brake, but not enough for a downshift? Trans fluid is at the correct level, looks pretty nice and red. I'll be adding a Magnefine filter shortly, doing a drain & fill, and adding a B&M external cooler in series. Have not tested this with 4wd engaged.

Also, is this something to be worried about?

Thanks!!

Bad Luck · 02-08-2023, 04:18 PM

Quote:

Originally Posted by AntonioCm1983

Hey everyone Check your Coils you could have a failing coil and the coil is working and as your slowing Down the coil looses power then regains Power and Current spikes on the secondary winding after recovery seen this on Cylinder 1 coil and because it's a waisted spark system 2 cylinders are loosing power momentarily and then recovering to fast for a misfire..... hope it helps all if you need coil ohm specs let me know....

I hope he hasn't been waiting for 2 years for your response lol

cl4Rk · 02-13-2023, 02:49 PM

Quote:

Originally Posted by AntonioCm1983

Hey everyone Check your Coils you could have a failing coil and the coil is working and as your slowing Down the coil looses power then regains Power and Current spikes on the secondary winding after recovery seen this on Cylinder 1 coil and because it's a waisted spark system 2 cylinders are loosing power momentarily and then recovering to fast for a misfire..... hope it helps all if you need coil ohm specs let me know....

Thanks for your reply, although this hasn’t happened for a couple years now since the frame swap..

brillo_76 · 02-14-2023, 10:39 AM

Maybe a bad ground issue that was addressed in the frame swap.

Sent from my SM-A536V using Tapatalk

4runherpow · 11-23-2024, 05:32 PM

Reviving an old thread.

I have a 4th GEN, but having a similar issue that I couldn’t find anywhere in the search. I read one of the symptoms and feel as if it’s similar to mine.

So when I’m coasting, if I press the brake, the RPMs will drop fairly quickly and then rebound with my foot comes off the brake. This is also an issue when I’m coasting at 30 to 40 mph and I do not hit the break but the RPMs will sometimes jump down and rebound up. I first noticed this because at highway speed I take my foot off of the accelerator and coast, when I put my foot back on to give it gas, it almost seems a little jerky as the RPMs jump back up.

At first, I thought it was my new muffler and exhaust maybe having less back pressure and thus having the RPMs drop, but I noticed I can re-create it with the braking and releasing of the brake. The RPMs will drop to below 1000 and then jump back up to 12 to 1400 RPMs while on the highway.

Is this a brake booster issue? That’s not allowing my RPMs to stay steady and higher at highway speeds?

Thanks in advance!

Site Navigation