2-1 downshift flare on 5R55E, TCC/EPC?

[mp223]

Hi all, 1999 5r55e with 150K on the clock, fluid replaced at ~75k and again with a filter at ~140k. Otherwise all original.

When slowing down to stop I'll get a bump in RPMs when the transmission shifts from 2-1, eg: foot off accelerator and on brake, 1000 RPM -> 1500 RPM -> downshift 2-1 -> RPM drop to ~600 while stopped and idling.

I tried searching but only came across 2-3 flare issues. Could this be a symptom of my TCC or EPC solenoids going? Also, how likely is the IAC causing this problem?

 

[BrooklynBay]

Did you ever replace the servos?

 

[mp223]

No. Everything is original.

 

[drdoom]

You may want to clean the throttle body, and check the associated linkage i.e. accelerator cable. Do a TPS test also.

 

[BrooklynBay]

Dried out servo pistons could cause a shift flare. Clean the bores & check for wear. Adjust the bands.

 

[mp223]

drdoom: Throttle body was cleaned thoroughly a couple of months ago. Throttle cable is tight, TPS read 0.97v at idle and 4.something at WOT. I'm gonna pickup a couple of junkyard IACs and see what that does, my idle has always been low at ~500rpm and I wondered if the IAC malfunctioning could cause a jump in RPM in specific circumstances.

BrooklynBay: I'm getting conflicting information, do I have to drop the pan to check the servo pistons? Is there a particular servo I should be checking, perhaps a picture? I will try the band adjustment first.

 

[BrooklynBay]

There are two servos on the side of the transmission which usually dry out. The one in the pan is much cooler so I wouldn't worry about the seals on it. The bands should be adjusted after the servos are replaced. Keep in mind that both servos are a different diameter, and the internal springs on each one have a different amount of tension. Do one at a time to avoid confusion.