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

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Jim

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

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

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?

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Jim