30sec for battery disconnect might not be enough time, try leaving it disconnected for a little longer next time. If you noticed a big difference in power after the disconnect ( reset) than you might have the same problem as me with negative fuel trims. You car is probably running lean at load
Unplugging the o2 will leave the car in the same state as right after the reset, so you should not have noticed any difference with them unplugged. Leaving them unplugged will keep the same state, your ECU will not apply fuel trims ever, in other words it will not try to detune your car at all but the negatives are that you might be using more fuel as with o2's unplugged it will run from preset maps and usually they are on the richer side, but this might be better than running lean.

You have tried a new MAF right? as this is one of the more common culprits of lost power on these cars.

 

This is exactly what my car is doing. Running lean...You can smell it. Yes, fuel trim is one of the codes I am getting. I have replaced everything else, and can't figure out what I have to do for the fuel trim. This is the only thing I have left for codes...Right now of course, all are still showing even though I've fixed it.

I've had these constant problems since the ownership of this car. I've done a lot and the symptoms have changed, but performance is still a problem.

I will go disconnect the battery for a few hours. what should I do with the O2 sensors?

 

Have you changed the MAF?

Usually around 30 min is enough for the disconnect/reset
plug your o2s back in
if you car runs much better right after disconnect, you can:
1. unplug the o2's and run without them, (I have been doing it had no problems but probably after that i would suggest to have custom tuning done just to make sure your Air/Fuel ratios are good and this will also add power as this will be a custom tune to your car) The unused O2's can be replaced by a wideband o2 so you can always monitor your own air/fuel ratios
2. keep disconnection the battery to bring lost power back, maybe install some sord of switch to disconnect power without having to unplug battery each time you shut your car off
3. you can try and get a new ECU as per the Mercedes Service bulletin as that might be a problem with your ECU. I have a used q3 newer ECU but wish i can find someone to program it to work with my vin number, dealer wants $1700 to refurbish a used ECU
4. i dont know

 

Yes. First thing I did

 

xlr8tin...I think one of your plugs might have gone south...or one of the plug wires have a short in it...

 

no way it can be that bad, I changed my plug wires 2 times...

 

Have you headed over to Benzworld.org's W210 E55 forum? Some of the guys over there are very experienced as well.

 

As another possible cause to the problem, is the TPS. You may want to change out the TPS (throttle position sensor) part cost about 130.00 and a 5 min. DIY

 

I will if I can't resolve this soon

Yes, that is one of the numerous things I've replaced

amgalex, I tried disconneting battery for a longer period of time. I ended up doing it for a few hours. I drove it to work which is about 25 miles away...Engine light was on. I parked it for 2 days and when I started it up today and drove it home the light was off the whole way. We'll see if it stays off though. Might be all it needed...

As far as power it seems good considering it's about 97 degrees with humidity at almost 100%. I make the long drive to Oregen next week and I'll really be able to tell during this drive how it is.

 

I had a 2000 W210 E55 about 9yrs ago that ran with no issues, but my buddies identical car is a slug. Its never ran right or like it should, never broke 100mph traps. It was very frustrating for the both of us trying to figure out its issues. He still has it and it runs strong with 100k++ miles. One of the best cars I ever owned, hands down.

 

Update::

something has made my low power issue a lot better , when driving around town now I can go for weeks without noticing low power issue and even after a few weeks low power issue is only at upper loads but not at WOT where it appears to be normal
After a while of driving and with monitoring o2 voltages and fuel trims here is what happens:
from about 55% load up to 82% or so O2s start to show car going in the lean direction and at the same time long term fuel trims go more and more negative in the (Open loop) which is weird because long term fuel trims at idle(closed loop) stay at around 0 or so. Ecu pulls fuel out in the upper load range starving the car for fuel but it is fine at WOT
my latest tinkering was with the EGR valve, I was doing a smoke test to check for vacuum leaks and have found few slight leaks in some hoses and a leak in the egr valve so I replaced with new EGR fixed the hoses and issue still remains still slight leak at EGR valve. When I monitor short term fuel trims and spray MAF cleaning fluid directly at the EGR short term fuel trim go to -2.5 indicating that there is slight vaccum leak at EGR. I read somewhere that slight leak at EGR valve is normal during smoke test, but I am getting some unmetered air into the system this cant be good, although I guess 02s should compensate.
So now I have tried disconnecting vacuum tube going into EGR and preventing EGR to open, plugged the vacuum tube up. Driving around this way
for 5 days now and I notice something weird that long term fuel trims are not correcting at all, although at the same time short term fuel trims are working just fine. Also I see timing being pulled back at cruise mode probably because of lack of EGR flow, although power remains good in the car and no long term correction..
I also have found some info that my opening up the exhaust and reducing back pressure this would have an effect on how long the EGR valve would remain open,,so who knows,,,( i have rear cats delete, x pipe and resonator delete)

so here it is

 

I am glad to hear you may have figured it out! The EGR is a very common and very hard to detect problem. It can act like a bad MAF and can leak at irregular times as it gets stuck. It seems to rarely throw codes. It is, for all intents and purposes, a "vacuum leak"- and a bigger one at that.

It is frequently overlooked.

I usually suggest blocking off the EGR as a standard practice when trouble shooting.

In hindsight it makes perfect sense.

After my smog check coming up, I will likely block mine off.

 

Just want to update this old thread! I still have the car and still have no power loss issues. The only thing that worked was disconnecting egr electrical connectors which will set off CEL light and but this stoping long term fuel trim correction . Stopping long term fuel trims was key!!

 

[QUOTE=amgalex;8445735]Just want to update this old thread! I still have the car and still have no power loss issues. The only thing that worked was disconnecting egr electrical connectors which will set off CEL light and but this stoping long term fuel trim correction . Stopping long term fuel trims was key!![/QUOTE

I think mine has this problem, is yours still running good?