underwhirled

I've searched the forum, but I can't really find an answer to my problem.

My 2005 C230 Sports Sedan is experiencing a weird problem. When the car is idling - say at a stop sign - the car usually hovers around 800 RPM. It has always done so. Lately about every 10 seconds or so, the RPM will dip say to about 600 and then quickly come back up to the 800RPM level. This is when the car is in drive.

It doesn't appear to have the problem as bad when it is in park. In park, the car idles around 1K and sometimes dips and comes back up.

I originally thought that this was only happening when the air conditioning was on, but it does happen when the air is off too. I took the car to the dealer. They replaced the plugs, wires, a couple of other items, and then we began to address the oil leaks that were starting around sever engine seals. 2,200 dollars later, I have the car back, but it still does the same thing. It doesn't throw any codes, and I'm wondering if this is normal.

I just don't remember the car ever really dipping in RPM like that at stop signs?

Any thoughts?

sammydragon3

u could be getting a check engine..if something happends it could take a while to show

how old is ur battery? air filters?....fuel filters?
put techron in only fuel cleaner approved by mercedes

oh ya about the car always being at 800 rpm at a stoplight thats WAAYYY TO HIGH

i had my car since new and its supposed to be at 500 rpm in drive...then 550 rpm in park

underwhirled

The battery has never been replaced, but all the filters have been changed. I'll try the techron.

xijonix

Honestly, mine has fluctuate like that when in drive from 600 to 500, and it's 70,000KM later it still does it and hasn't hinder performance and hasn't risen any engine problems. So I say don't worry about it and just enjoy your car.

... 800 does seem a tad bit high but it depends on the engine 2.6L V6 idles around 600to500 at stoplights, my cousins c230 4CYL idles 800 so I don't know what to say in terms of idle RPM seems to be engine dependant. In terms of fluctuation I say it's normal, don't worry about it or you'll keep tossing money into the pit.

I am considering changing my spark plugs if you haven't you may want to consider depending on how old the spark plugs are. Mine is the original has about 180000K on the original spark plugs so I say sometime it would be good to change it out. Changing old nasty spark plugs for new ones usually in a good bit of cases result in smoother idle.

LILBENZ230

Wtf Sammy.. "you could be getting a check engine"? I think he would know if the CEL was coming on. He says it does not have codes.

Have you cleaned the MAF? Replaced the O2 sensors? How many miles do you have? Mine will dip now and then and recover, but constantly is definitely not right.

sammydragon3

when i had oil in the ecu and the connectors i had it dip lots of times

and i never got a check engine for like a week after

Russell Ormerod

usually a mixture problem, engine is too lean. check for airleaks airleaks airleaks. when they are right it should not hunt at all.
Once you have fixed any air leaks service the throttle body have all adaptations reset, and you good to go.

nlpamg

mine fluctuates when it's cold, but it doesn't affect performance at all. just annoying and weird. my plugs were replaced not too long ago. can't figure out whats wrong. hopefully it's not the throttle body, again.

fookoo303

Mine does this often too and I replaced the plugs, wires, cleaned maf, and run techron through regularly. It never goes away and I can't find a solution. I just learned to live with it.

underwhirled

I got tied up with work the last couple of days, and I haven't really been leaving the office often.

I haven't tried the techron yet, but I do still have the problem. This morning when I went to leave my garage, the car noticeably shook roughly while the car was in the driveway. I can live with a bit of a fluctuation, but the car has about 106,000 miles on it. They did change the plugs and wires, as well as several oil gaskets that needed to be replaced.

I guess it's frustrating because the car has always ran so smooth. Anyone would have noticed this behavior. I may take it back to the dealer tomorrow and have them take another look. I could wait to see if something breaks down, but prevention is more my style. Noise is friction. Friction is wear, and wear is money. This isn't a noise, but I'm sure if I let it go longer it will cost even more money to fix.

LILBENZ230

Let us know the end result..

underwhirled

OK, I have the car back. And, yes, I took it back to the shop to have it looked at again. The car wouldn't do it in the service bay. Very annoying. I think that I have found that it really is tied to the air conditioning system. It feels almost like the AC compressor is introducing a load intermittently. I know they replaced an air conditioning part a few months back - not the compressor. Is there a belt that could be slipping or a tension mechanism that could be set incorrectly?

underwhirled

Well, here we go.

It is apparently a butterfly valve within the Throttle Body assembly that is not closing properly. The new part - wait for it - with the hour labor is going to be $1,650.00.

shaystudies

My car did that, when the AC was on. I was told that it was the broken engine mounts kind of weird but i got the service done and now its fine=)

shaystudies

Oh! and i got that service done at around 98K now my car has 128K

LILBENZ230

The engine mounts really smooth the engine out. Doesn't mean the dip will go away, but it does smooth out.

Underwhirled, that is highway robbery. Yes the throttle body is expensive but that is ridiculous. You could easily DIY. Here is the part for $736:

http://www.rmeuropean.com/Part-Numbe..._94E6B777.aspx