eldridge173

Hello all first post so bare with me,

i recently purchased 1999 ML320 that is 270,000 miles young. I've had 20+ BMWs, but this is only my 3rd merecedes (420 sel years ago and a 05 sprinter) so I've got a question that i couldn't get a firm from searching so if figured i need to post it up.


So my ML does the typical you read about where it idles a little rough when you put in in drive or reverse, i think but i am not sure that is due to a low idle (just a hare over 500 rmps in gear), but what im curious is even when it is in neutral it will randomly drop and drop very low, occasionally it will throw a CEL as it did this morning when it did it idling in my parking spot at work in neutral. it does this with out the AC running so we can eliminate that possibility.....hopefully.

So far i have changed the plugs, they all burned very evenly, zero black build up or oil what so ever, serviced the diffs and Tcase, air filter, and ran some injector cleaner through it, replaced valve cover gasket, and center support bearing. From what i can tell two of the cats have been replaced they are dated 4/09, and it is a two owner car with service history from day one, and it appears to we well taken care of. so the last time it did this the codes were 0410 and 0130 so secondary air in injection and o2 sensor bank 1 sensor 1. ill go read the codes at lunch and see if they match the previous it threw about 600 miles ago, but give it did it when the idle droped super low i would guess it is the same.

short of that this thing runs like a dream, doesnt burn a drop of oil, all suspension components are super tight, trans shifts perfect, no Tcase noise, i really like this old beast. any help would be greatly appreciated

Thanks, Brandon

Plutoe

Your idle control is all accomplished my the engine ECU which receives numerous signals form numerous sensors--there as you have learned the fault codes are very important in diagnosing the problem---post the faults!!

eldridge173

ok so only one code popped the 0410 secondary air code, it seems intermittent being it kicked on again after a good while

Plutoe

There are about four items in that system and as you know the system is apart of the cold start emissions control system--if you hear the motor and fan run then the 410 typically is the switch over valve--however without the test equipment you could or can change out the wrong component and be back in a more expensive boat with the same problem!!