Intake manifold vacuum numbers ? on 04 ML350
 

I've got an ML350 in (241k miles) that I've been helping the owner get in good nick. The customer indicated that he thinks that the truck is "shuddering" at idle sometimes. When I was watching actual values the intake manifold pressures were occasionally out of spec. Could this be an indication of plugged cats?

Is there an easy way to check for plugged cats? I am not getting any fault codes. I do plan on changing the engine/transmission mounts.

Other than the shuddering it looks like it probably uses a little oil and it runs/drives out good.

tia

Probably not cats. I'd look into vacuum leaks where the intake manifold flap actuators pivot. It may need a manifold.

hmm, I'll look at that. Sometimes I hear a sound that sounds like a messed up window regulator (broken plastic gears) at the rear, passenger side of the engine. I see the manifold flap at the front drivers side of the intake. Is there one on the passenger rear too?