2004 V70 occasionally stalls when your foot is completely off the throttle. it will generally happen when slowing for a turn or stop. It restarts easily & immediately.


Other than this, car runs perfectly. It did generate a code some time ago about Catalytic Convertor efficiency, but that has not recurred.


Thoughts?

 

I have some more info. The transmission appears to play a role in this.... At least the part where the engine idles low enough that it can stall. Here is the behavior;


1.) Start with the fact that stopped at idle & in gear, the engine idles at 750 RPM. So that is an engine turning against a torque convertor with its output shaft stationary (and Torque Convertor clutch unlocked).


2.) as the car decelerates from speed to a stop (either breaking or coasting) there is strange routine.
- Above 30mph the engine turns 750rpm or higher
- As we slow through 30mph, engine drops to 500rpm (suddenly)
- As we cross 10mph, engine pops up to 750rpm


4.) While the engine is turning 500rpm, I can feel a significant vibration from it turning so slow.


5.) If you just touch the throttle during this 500rpm phase, rpm's hop up feely, settle back to 750, then in a second, snap down to 500


6.) If you put the car in neutral to slow, the engine just goes to 750rpm & stays there.


My conclusion on the cause of the 500rpm is that the torque convertor clutch must be locked at that point & the transmission has gone to a low enough gear that the locked convertor & transmission are loading the engine down.


For note #5 above, here is what I think the Convertor clutch is doing...


5.) If you just touch the throttle during this 500rpm phase, rpm's hop up feely (Clutch is commanded to unlock on throttle), settle back to 750 (Clutch is still unlocked), then in a second, snap down to 500 (Clutch is commanded to lock up again)


Does this make sense?
Does anyone else's car do anything like this?


Mike

 

Same thing happened to my v70 non turbo, try cleaning your throttle body, that worked for me.....

 

Actually it was the throttle body! All my speculation about the transmission was wrong. Pulled & cleaned the Throttle Body and the problem disappeared completely.