RPM's rev up and down

[mtenderenda]

I notice when I let off the gas, while coasting down a hill or on the highway, the RPM's rev up and down. Wondering if someone else ran into a simular situation. What can i try to fix this?

[glassman99]

It sounds like your torque converter is locking and unlocking. This can be cured via programming.

[ROB502]

Mine did from factory and still do'es it with a tune but not as bad.

[Big House]

If a tune can fix this...let me kow. I have had this little issue for a year or two. My fix...I stay on the GAS:burnout:

[TooManyFords]

I notice when I let off the gas, while coasting down a hill or on the highway, the RPM's rev up and down. Wondering if someone else ran into a simular situation. What can i try to fix this?

This is a function of a timer delay in the PCM to unlock the converter when coasting. I think the default is 10 seconds before it begins to turn on and off the injectors to save fuel. This is the rpm hunting you are experiencing.

It is programmed in and normal. What may not be normal is if the tune has changed the time delay to unlock. You can try it yourself and count to see what it is set to.

John

[mtenderenda]

Thanks for the fast responses guys...SO if it's not broken, then don't fix.
Now if I went ahead and purchased a supercharger, then I would use the Tune and get rid of the reving. It doesn't bother me, i was just wondering about it. I've had the car now for 2 years, I just noticed it doing this..

[Big House]

I didn't notice mines until I got my exhaust done. After that, I just stay in the gas.

[JohnE]

It's not likely that the torque converter is being locked and unlocked.

Typical cause of rpm surging while coasting and the torque converter is unlocked lies in dashpot settings. The dashpot controls the bleed off of air through the air air control valve. It is supposed to gradually pull air to make a controlled coast down. There are multiple factors involved in dashpot. There is a rate of decrease. There is also a starting point for air demand and two lower limits, one for RPM and one for vehicle speed. The bouncing is result of the PCM oscillating between upper and lower limits, due to the air settings.

It's likely to have this issue after changing the stall of the torque converter. A higher stall converter will give less assistance to help turn the engine over while coasting down at highway speeds.

This rpm surge is annoying, but doesn't really hurt anything.



John