NOTE LOOKED UP THE VIN - IT' S a 2002. Working on a 2002 E320 4matic, W211.282. 100K miles, deceent maintenance. Complaint was high and rought idle. Started off with codes for oxygen sensors, lean mixture, EGR malfunction. Replaced oxygen sensors and MAF as maintenance items. Now left with P071 (lean left bank). Idles in Park at about 1500, but here is the weirdness - if you depress the brake pedal, the idle speed drops to 750.

The EGR valves hold vacuum, and at idle the switch is not allowing vacuum to the valves. There were some minor tears in the hoses for the crankcase ventilation system, but nothing major. Spraying brake cleaner around the intake manifold and injectors produced only minor effects on the idle.

Anybody seen this before? I am thinking a bad brake booster, but the brakes are fine and it's been my experience is that a bad booster will increase the idle speed when the brakes are applied.

Thanks,

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

The brake booster vacuum line connection is on the right side of the intake at the back (if you're looking at the engine from the front, so it's nearest to the left bank). The fitting is kind of funky and the plastic insert gets old and can crack, causing a vacuum leak.

In any event, that's something to check, maybe just disconnect the booster vacuum line and plug the manifold connection as a test.

Was prepared to somehow get the vacuum line out of the booster, but the high idle stopped and went back to just plain lumpy.

Took the car to a shop and had a full SDS readout. No component malfunction but a recommendation to replace the four breather hoses and return for a smoke test if that doesn't help. Also recommended replace the EGR valve and pipe as it is generally clogged on these cars with 100k+ miles.

After driving the car, noticed that the lumpy idle is intermittent. Leaving the shop, there was a small amount of vibration at idle that I would have thought was motor mounts. Ten minutes later, it was shaking to the point where I couldn't understand how it could keep running.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

The P0400 EGR malfunction code came back, so I replaced the valve and the tube. Problem solved.

The only advice I can offer is that the tube is fairly easy to remove and clean out, so I wouldn't replace it as a matter of course. If you do replace it, be sure to get the little compression fitting that goes on the valve end of the tube. There are also two gaskets that should be replaced. If you remove the connector on #3 fuel injector, it makes it easier to get a socket on the front screw that holds the valve to the head.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe