Odd tach readings on deceleration

[HerNameIsLucy]

Many years ago I started shifting automatic transmissions on all the cars and trucks I've owned into neutral when I'm braking and won't be needing engine braking help. It helps on wear on the brakes, and saves me a drop or two in gas by letting the engine return to idle before I come to a stop.

On my 02 taco, if I'm doing say 40MPH, see a red light ahead, and put it in neutral, the RPMs go down some, but not much. They don't return to idle speed until I am stopped.

I can understand if this is normal behavior if it is by design, it would keep the tranny in closer sync to the engine should I need to shift back into drive before stopping.

But, is it normal behavior?

If not, could a sensor somewhere be not telling the ecu to let the engine return to idle?

[HighDesert]

The ECU directs the idle speed control to adjust for fast idle, warm curb idle, air conditioner load, electrical load, and automatic transmission load. Your higher idle could be the result of a cold engine, emissions control, or simply the automatic transmission adjusting to the neutral state. You can always dump your ECU codes to see if you have a failure state. Or, given that you like to shift, maybe you are a prime candidate for a manual tranny

[chris4x4]

Originally Posted by HerNameIsLucy

Many years ago I started shifting automatic transmissions on all the cars and trucks I've owned into neutral when I'm braking and won't be needing engine braking help. It helps on wear on the brakes, and saves me a drop or two in gas by letting the engine return to idle before I come to a stop.

On my 02 taco, if I'm doing say 40MPH, see a red light ahead, and put it in neutral, the RPMs go down some, but not much. They don't return to idle speed until I am stopped.

I can understand if this is normal behavior if it is by design, it would keep the tranny in closer sync to the engine should I need to shift back into drive before stopping.

But, is it normal behavior?

If not, could a sensor somewhere be not telling the ecu to let the engine return to idle?

I wouldnt be putting the tranny in neutral and coasting. When you do this, the tranny looses fluid pressure, as the fluid pressure is pumped by the input from the engine. You could be overheating your tranny, and the ECU is trying to control it by upping the rpm's. Me thinks it would be in your best interest to keep it in "D", or continue to shift manually and avoid shifting into "N" until you are stopped.

[HerNameIsLucy]

Interesting replies. I'm still old Ford school, where the tranny pump runs in everything but park. Didn't consider might be pissing the tranny off shifting to neutral.

Next trip to AutoZone I'll borrow their scanner and see if there's anything in there.

Autos got me spoiled, but manuals are fun!

Thanks

[chris4x4]

Originally Posted by HerNameIsLucy

Interesting replies. I'm still old Ford school, where the tranny pump runs in everything but park. Didn't consider might be pissing the tranny off shifting to neutral.

Next trip to AutoZone I'll borrow their scanner and see if there's anything in there.

Autos got me spoiled, but manuals are fun!

Thanks

The tranny pump is still "running", but not putting out the required psi when shifted to neutral while in motion, thus causing the engine to try and compensate. Its not going to throw a code, but I dont think its very good for the tranny to continue this. I have run accross similar tranny behaveior in My Dodge and some other vehicles when bumped into neutral by accident.