Both my cars went down so I borrowed my friends 99 626. When driving it, I noticed that it shifted erratically & also accelerated poorly, until I lifted off the pedal. Wont go over 45 or 50 max. Also I notice a whirring sound when I accelerate almost like a turbo spooling up & as soon as I let off the gas pedal, it stops. Thought that could be a vacuum leak. I cleaned the MAF sensor thinking it might be dirty & also looked around for any vacuum hoses that may be off, cracked or missing. Couldn't see many hoses let alone any damaged ones.

Trans was rebuilt by a reputable shop 3 years ago.

Trans fluid seems fine; pink, good level on dipstick & no burnt smell.

Thoughts?

 

May be associated with a blocked exhaust. You can take out the upstream O2 sensor (if it has one) and take it for a drive but pay attention to where the hot exhaust gases a blowing. You may need to make a small heat shield.

 

Rogue626 Welcome to the forum