2004 CTT hard downshift

[Zakowsky]

So I took my new to me 2004 CTT for my first real longish drive in it today (4 hours), and noticed a new problem. After running on the highway for a while, occasionally on the faster side (140-150 kph), when I would go to slow down I would get jarring downshifts from 5-4, and occasionally from 4-3. Turning the PSM off got rid of it, and it doesn’t happen in normal city driving or cruising at more prescribed speeds like 110 kph. Now, I’ve read all the info about the transmission valve body going bad, but mine was replaced not long ago. Does this suggest anything other than a serious transmission issue, like the tranny fluid should be changed or there is a vacuum leak somewhere? It also seems really determined to learn my driving style when the PSM is on; accelerate hard a few times and the shift points move up for the next few minutes – could this be a training related phenomena? I usually leave the PSM on; goes great with it off but it really kills my mileage! Thanks.

[ekstroemtj]

As i remember you was working on the air tubes some days ago?!

[Zakowsky]

Yes; are you thinking a vacuum leak could do this? The work on the MAFs was somewhat successful – after draining the oil from the intercooler hose I cleaned the MAFs yet again, and this time it seems to be lasting longer. The idle gets rough much less often, and starting has been better overall. But I do suspect some airline problem, as it now does sink to 400 rpm then pick back up again to 580, which is often a sign of a vacuum issue. So I’m thinking since the transmission hard downshift is only after the throttle has been open a lot, the two could be related. Just not sure which lines might be the culprit. I guess a smoke test is in order.

[ekstroemtj]

Yes there is a relation between. 

Idle, rpm and shifting is all togehter.  Maybe some of the professionals here can explain how.

but my own experience is showing this very clear.