Hey.
I’m having very disturbing issue with my 2003 Volvo XC90 2.5T.

When cruising and overtaking at city speeds all is ok.
When trying to overtake someone on highway (100km/h / 60mph), pressing accelerator makes the whole car shake as if axle splines would try to make contact with transmission or wheel bearing. The shaking goes for 1-1.5secs and then the car downshifts to 4th or 3rd depending on how far I pressed pedal and starts to build up speed.
While shaking, revs dont change but stays the same.

1- when i downshift manually from 5th to 4th in MAN mode, all is ok, there is no shaking. The shake is only when in automatic shift mode.
2 - if accelerating while cruising at 120-130 km/h there is no shaking, it downshifts really well by itself
3 - have drained the gearbox for 2 times now this month, doesnt seem to have milky texture if coolant would be present in atf. Will do drain and fill 3 more times to make gearbox cleaner. Shifting is really smooth and good for car this age except that one bit on highway
4 - when cruising in 5th gear around 2000rpms there is this low pitched vibration. If shifted to 4th gear, revs go a bit up and vibrating sound eliminates. I don’t wanna drive in 4th because of fuel economy. What that could be? I changed both rear wheel bearings a month ago. No change.

has anyone had this shifting issue?
what could it be?

front right driveshaft bearing?
propshaft center holder bearing?
sparkplugs?
throttle body?

 

How old and what brand is your RF axle?

When the inner CV joint wears that symptom can be present. Shaking/rumbling when lightly accelerating at ~60 mph. Under hard acceleration the shaking/rumbling will go away or not be as noticeable. The solution is a replacement axle. Be cautious, there are many crappy brands out there - sometimes the "new" axle shakes worse than the old one!

I would recommend the GKN axle brand - They cost more but are worth it -

 

Don’t really know the state of RF axle. Probably old.

Also, just happened. When tried to overtake it started with the shaking and then suddenly ‘Reduced Engine performance’ and it wouldn’t let me accelerate. Stopped, restarted the engine. No CEL, no Reduced perfomance error, but still shaking in the 5th.

could it be spark plug/coil related not drivetrain? From the severity of shake I think it might be axle, but axle wouldnt give me reduced performance error, would it?

 

You should scan the car with an appropriate scan tool - in an attempt to figure out what caused the warning text. How old and what brand are the spark plugs? Or could be an air leak that only occurs under heavy boost - the intercooler hose near the alternator gets pickled and soft sometimes -

A worn cv joint will not produced that error message - or any message

 

I have appointment with my Volvo specified electrician next week.

I think that reduced power message came up because I was running out of LPG when accelerating and it didn’t have time to switch back to gasoline when I was accelerating so my guess the error might be something about running lean.


Last time when I took car for diagnostic, the VIDA showed code for boost pressure valve. But the mech said that the code is not active and will look at it if it comes up any time again, till that I should leave it alone. Could that be the shaking culprit? Or more possible that axle is bad?