I changed the transmission fluid and included a bottle of Lucas during the refill. Transmission is smoother during changes, but at idle in drive, the RPMs will occasionally drop low, and on one occasion it cut off at a stop light.

I'm not sure what would be causing it. I did this same change (including the Lucas) about 5 years ago, and I had no issues afterwards.

Thoughts?

 

Idle air control valve or throttle position sensor. They were notorious on the fords 5.4litres.

 

My thoughts are that it's coincidental. I have however seen torque converter issues cause similar symptoms.

 

That would explain the low RPMs, but any idea why it would start after a trans fluid change?

 

I'm hoping it's coincidental, but it certainly wasn't doing it before the change, and it's definitely doing it after.

I wonder if it would help if I disconnected the battery to reset everything and let the ecu relearn proper idle?

 

Worth a shot

 

What trans fluid did you use? You mentioned the Lucas, but not the fluid. I always use Dex 6, which is thinner than the specified Dex 3, and add the Lucas, reasoning that the resulting thicker mixture is just about right. I've never had a problem.

 

I'd take the idle air control valve off and then spray the inside real good with carb cleaner and then dump the gunk out and keep doing that until the gunk it all gone then let it dry for a few and re install it

 

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