Please help! My '03 C230 is revving during a cold start. It revs for about 45 seconds before leveling out. Here's a video to show you what's happening:


Once it warms up, it drives fine. There is no CEL or DTC codes stored. This problem has been ongoing for quite some time. I was originally told that the cat needed to be replaced, but I have been told by a smog tech that the cat is working fine. The service bulletins have been taken care of and I have cleaned the throttle body. I have subsequently replaced the coils, the plugs, the oil, and the MAF. I have a new air filter on order and I have tested for vacuum leaks, and I am thinking now the problem has to do with the Secondary Air Injection system. There is an Air Injection/Exhaust Gas Recirculation Valve (round silver valve at the front corner of the engine cover). There is also a small blue plastic inline check valve under the plastic engine cover and a switchover valve. I am wondering if these parts might be causing my problem. Any feedback is greatly appreciated. I am planning on cleaning them to see if that does anything, but I'm guessing they might need to be replaced. Thanks!

 

Tried cleaning them with throttle body cleaner. The recirculation valve is pretty gunked up. I could blow through the little blue check valve in one direction very easily, but after trying to clean it, it seems harder to blow through. I probably made things worse. The car still revs, but now it idles worse after it warms up. Maybe I'm on to something. Are these dealer parts only? By the way, the car smells like exhaust gas during the first minute. It definitely seems like the cat is not working until it gets warmed up a little. Its got to be this secondary air deal, I hope. Thoughts?

 

I have the very same problem...... exactly as you've described it.


In my case, I am actually now getting P0410 code.


So yes, it seems the "secondary air injection system" is the culprit.


I've had these (what you described in your first post) symptoms for about 2 years.
I simply chose to "live with it" (give it 2 minutes after cold crank to settle) as there was no code thrown.

This month, a P0410 code showed up twice with a CEL.
After clearing it the first time, it showed up again in approx 2 weeks.


Please post feedback if you do get it fixed.

 

I would say my symptoms probably started almost two years ago as well. After a year, things really got bad and misfire codes were being thrown all over the place. The car started losing power and that's about the time I took it in for the service bulletin repairs. That's also when I discovered a bad coil and spark plug and when I was told I needed a new cat. The indie shop wanted $2500 to do the repairs, so I took it home. After that, the car was sidelined when my wife and I had our third child last year. Now, I'm trying to get the car back in shape and the cat seems to be fine. I'd like to get it fixed soon, but before I start replacing the Secondary Injection parts, I want to get some feedback from anyone who has actually fixed this problem. I'm sure we're not the only two....

My understanding is that the 4 cylinders do not have an air pump like most other MB's, it just has the three main valves mentioned above. I'd change them today if I thought it would fix the problem, but I'd like some reassurance. I also believe it could be a build up of carbon in the exhaust manifold. Any experts out there?

 

Can someone offer some suggestions on what I should check next? Thanks!

 

I've actually had similar problems with my car during the winter. I brought my car in for a service and afterwards the problem got worse. I didn't bring it to a MB dealer though, I brought it to another garage that specifically works on MB vehicles.. the guy had no clue what it was.. he suspected the spark plugs so he changed those but the problem is still there. I haven't had the opportunity to bring it back yet, but I too would like to know if anyone was able to find a solution for this. I was able to search some similar scenarios on the forum but no real solutions.

 

sadly, all I can say is that I've been having the exact same issue also
when I rev it, it goes away for a few seconds, then comes back for a bit, then goes away. It might have something to do with a cold cat, but IDK!

 

I made a thread before with a similar problem/video. I used to have a similar problem but solved it by doing a bit of cleaning. I bought a "fuel system tune up kit" by 3M off amazon for 26 dollars. While using the cleaning agents my car was misfiring and blowing really bad smelling white smoke. (my engine was probably really dirty) Don't go changing you're cat before you try this!