Hello all,

I have posted here before but I couldn't remember my log in credentials so I started a new account.

We have a 2006 XC70 that over the past several months had a very slow downshift and a major clunk when it dropped into gear. It was diagnosed as a bad valve body in the transmission so we had it fixed and over the last few weeks the transmission is working very well with an odd stumble once in a while (which we were told it would do as the computer learns our driving patterns).

The new problem we have is that every few days when accelerating the rpms will suddenly drop (to idle speed?) as if the throttle cable/wire (whatever it is) breaks. It only last for about 1 second and then the rpms bounce back up to where they should be. The last time it happened it did it twice in a row, 1 sec rpm rapid drop, 1 second rpm bounce back, 1 second rpm rapid drop, and then rapid bounce back to normal. When this occurs I think I can also hear a thunk noise as the transmission is driven again when the rpms bounce back.

I have no clue what is happening. My fear is that if I take it to the repair shop it won't happen to them and I will have wasted another few hours shuttling the car back and forth. Does anyone here have any idea what is happening and/or what I should be looking for? Is this the kind of thing that would show up as a code if the repair shop checks the computer?

TIA,
Blane

 

2 things i can think of - the CEM can get water damage and make weird things happen - Or the wiring to the throttle body gets a bad connection. Volvo has a service solution, some of the wiring is replace at the throttle body. There might be codes stored - but this problem went unsolved for years until someone figured it out. Cars with random miss-fires or lack of throttle response. Attached youtube has part numbers

On your valve body - if you or your shop has VIDA or a compatible scan tool - The transmission/TCU can be put into adaptation mode - the car is then driven in a specific manner for about 45 minutes to get the TCU to learn the best way to shift. I did that will all replacement transmissions I put in. Some cars I offered a valve body only - but no one wanted to take the chance. I put a valve body in one of my personal cars and it was 90% fixed.

 

Just a quick follow-up to the issue I was having. Thanks to the help and recommendations of the forum members I replaced the fuel rail pressure sensor and since that time have not had the issue with sudden and short loss of power. It appears the sensor was the cause of the problem.

Thanks again for all the replies I received

BWSwede

 

You have two independent issues. One is the shift solenoids in the transmission, the second is a throttle body that needs a good cleaning.

However, you have to decide what you want to do.

 

Tony,
Thanks for the reply and advice. Everything is working fine since we replaced the fuel rail pressure sensor. However, if it acts up again I'll look into your suggestions.

Best,
BWSwede