TCM Replacement Follow Up

[steveroberts]

Thanks to friends on this forum, I successfully replaced the TCM on my 08 Mazda5 Touring.

In general, the transmission is shifting more smoothly than it has is a while. However, on rare occasion, when I stop the vehicle, it goes into a very rough, shuddering idle. This generally goes away on acceleration.

Just wondering if there is anything to be done about this.

Thanks for any suggestions you may have.

SR

 

[negusm]

Bad/violent idle is usually an engine issue. This can be a bunch of stuff.

Bad engine/transmission mounts.
Bad injector(s).
Bad spark plugs/wires.

Any codes thrown?

 

[steveroberts]

Thanks for your response.

Engine mounts recently replaced. And no codes.

This is a very intermittent problem and is mostly absent. Was thinking TCM as another post on the subject mentioned rough idle immediately after the TCM was installed and that the TCM self-programmed after running for a few minutes and then smoothed out.

 

[negusm]

How does a TCM affect idle? That doesn't make a whole lot of sense to me, but newer cars being what they are...who knows?

 

[steveroberts]

Took the car out today; first time in a couple of days. I think the "rough idle" is a tendency to stall at a stop. It happened once over the course of a 20-minute drive. Engine cut out after RPM went below 500 according to the tach.

 

[negusm]

I would look at the MAF, IAC and TPS along with Vacuum leaks.

Vacuum leaks can cause issues. Do the Starter Fluid spray test and see if idle improves during the test.

Cleaning the MAF is cheap but you may need to replace it.

The IAC gets a ton of exhaust gases that clog it up, so that may need replacing.

A TPS going bad can cause issues too.

Throttle body may need cleaning.

 

[steveroberts]

Many thanks!

 

[Silentnoise713]

Are you only having the idle issue when the car is warmed up to temp?

My suspicions:
1) Vacuum leak, a seal or plastic crack someone on the intake or hose side that is expanding, ever so slight to let air in when the car is up to temp
----intake manifold/intake gasket
----EGR/gasket

2) My biggest concern is signs of torque convert wear/tear. I'm no trans expert but I learn that when cold, the TC does not lock up (to get car warmer). Tried changing trans fluid with no success.

FWIW, I've come across quite a few Mazda3 posts with the issue and NO ONE has been able to resolve it.

 

[teetee1]

Did you let the car relearn the ideal speed after disconnecting the battery from TCM replacement?

Check out YouTube for computer relearn for modern mazda's. I remember you just need to rest the computer (battery disconnect / reconnect) then just let it idle with lightest power draw load and the most power draw load, 20min each and you are good to go.

Something like this:

Fix Your Mazda 3 Stalling Running Rough

If you've got a Mazda thats been acting funny, idling rough, stalling you may want to try this fix before getting the tune up, fuel filter change, throttle b...

youtu.be