Just encountered something on my way home from work. Sitting at an intersection my CEL came on. When I let the engine rev to upper revs it has lost the power it had before. The engine will rev but with no additional power. Everything is smooth and nothing is acting out of the ordinary except the loss of power. After coming home and popping the hood I noticed that the intake flap at the location of the EGR valve isn't fluttering like it normally does at idle.

Does this sound like a possible vacuum problem? I don't remember if it was there before but I hear a light Psssssss from underneath the black valve cover cover behind where the crossover tube goes over?

I'm gonna take the crossover intake tube off tomorrow and I would like to clean out the interior of the tube and possibly the intake plenum if I get that bold. What is safe to use on this "aluminum". I was thinking about using brake cleaner.

What size torx socket is needed for the bolts on the intake?

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'97 E300
'99 E300

My bet is that your mass airflow sensor has kicked the bucket. This happened to an E300 DT that I was selling for someone a while back (I don't remember the mileage). IIRC, the new part was ~$300. This is a common failure item on the VW TDIs as well.

edit: a computer diagnostic check will pinpoint the problem for you.