RMP's drop when shift from park to drive/reverse

Need some help guys, I tried to search around for an answer but came up with nothing so far. When I shift from park to drive or reverse the rpm's drop around 800rpm to just above 500rpm. never used to go that low and is causing the truck to vibrate when coming to a stop. Shift to park and the rpm's go back to normal. No codes, no stuttering of acceleration or any other symptons, accelerates fine and stays good when under throttle. Starts up first try. Tried to do basic stuff like new air filter, cleaned maf sensor, cleaned throttle body. Was thinking I should check transmission fluid level but I changed it months ago and rpm was fine and also thinking throttle position sensor is bad but again the rpms are fine when in park so makes me think its not those things. Its just a confusing situation because it idles great when in park. any ideas guys?

 

Year and mileage would be good information to add. It sounds like this started happening after you changed the transmission fluid, correct? The first thing I would do in that case would be to check the level again and make sure you're good there. Issues caused by low transmission fluid levels don't pop up immediately from my experience.

 

2018 80k miles. I will check it tomorrow. I did do it in the summer heat. after a drain and fill I opened the level check bolt and closed it when there was only a trickle stream of fluid coming out. Maybe the cold weather has made the fluid compress below proper level. I do wonder how a low fluid level in the transmission would make the rpm's normal in park vs in drive/reverse...no pressure in the case when its in park? also when the tranny fluid is heated up to normal temp the rpm's in drive/reverse are still abnormal which leads me to think its not the tranny fluid. no slippage of the gears or hesitation either. I'll see if adding a little more fluid helps.

 

I wouldn’t add any fluid unless the level is low. Check the level first and go from there.

 

Narrowed down the problem. The RPMs drop when I'm in drive/reverse when only brakes are applied. Seems like its a brake vacuum line leak or a bad brake booster causing the rpms to drop when I apply brakes. When I put it into drive and put on the e-brake and let go of foot brake the rpms return to normal, so indeed it is a vacuum leak causing this drop in RPM's. Just posting this so other people can see it in the future. I will soon post my solution, hopefully its just a bad vacuum line and not the brake booster.

 

Replaced new oem brake booster, cleaned injectors...still rpm drops to 550/600 when at stop in drive/reverse. checked for vacuum leak on the intake to booster line, looks good. ran out of options now. seeing if anyone else has a suggestion.

 

What you're describing is normal. With the engine running in Park or Neutral the engine is under no load. When you shift into a gear the engine is now under a load even though it isn't moving. RPM's are going to drop. I've never owned a vehicle that didn't do that. My Tacoma has about the same RPM's under load and with no load as yours. It's been that way since new.

I don't know how to do it on a newer vehicle, but there used to be an idle adjustment to change the idle speed on older vehicles. I'd assume there is some way to do so on a newer truck if you just want a faster idle speed.

 

thanks for the input. at this point its been going on for so long it feels normal haha. just uncomfortable when truck is vibrating at 550/600rpm. plus it didnt used to be like that. cant adjust idle manually on the 3rd gen but im going to look into if it can be adjusted with the ECU using techstream.

 

Maybe try cleaning MAF and throttlebody?

 

cleaned maf, cleaned TB, replaced gasket, replaced plugs, cleaned injectors, unplugged all electrical accessories and checked ground, new altenator. ive done all i can. only thing im going to try now is check level of trans fluid but thats desperate. would be nice to see if techstream can adjust idle rpm undet drive/reverse.

 

Fk...

 

You are chasing a nonexistent problem.
What you describe is normal.
Neutral and Park will have a higher RPM. In gear it will be lower. Between 500-600 RPM.

Here is the data from the FSM

 

Need to fix title

 

my truck didnt idle like this before thats why im concerned. i just dont think 550 rpm is normal idle. im auto trans with ott tune. the prob seems to be involving the brakes, thats when it bogs down only in drive/reverse. also belt makes screeching sound as it bogs and stays in low rpm. i changed to new oem belt.

 

Set the parking brake. Shift in to drive, let foot off brake pedal.
The parking brake should hold the truck back. See what happens then.
If the idle still drops, it's NOT a brake issue.

 

yep i have experimented with that, idle goes back to normal when i let off brake in drive/reverse. rpm bogs down only when i apply brake. hard to research about this because every topic about this situation only has two answers "its a vacuum leak, its your brake booster"...almost makes me think its an electrical issue perhaps because i got no other options. I have the meso customs tailight LED harness installed so I will try to put back in stock bulbs but i doubt its the issue. I will also post in the OTT tune thread as I have their tune but it never was like this when i got the tune.

 

We do not adjust the idle settings in any way on any of our 3G calibrations.

 

thanks for the info, saves me some time.

 

replaced the fan clutch and low rpm still there when pressing brake in D or R. It's really unfortunate this experience has really been ruining the whole "toyota reliability" thing for me. Could this be a torque converter problem? Just really trying to think why it only happens when I press the brake in D or R.

 

Toyotas are notorious for idling low when hot in drive. Yes they shake a bit but if it's not stalling and dying at stop lights then you don't have a problem

If you had a vacuum leak through the booster you would have seen the fuel trims jump up positive when pressing the brake. You should've checked that before throwing a brake booster at it.

Did the new belt take care of the squealing noise? If it's still squealing you could look at a possible seized A/C compressor dragging the rpms down. That doesn't mean throw a compressor at it, just a possibility..