Steve_Kaboom

I have a W204 and recently had an engine light come on. After having the code read, found that it is a P0410 secondary air injection system malfunction. I have done some research into this code and found that in most cases, where the secondary air pump is going bad, if makes a "jet engine" sound for about a minute after first starting the car. However, these are not the symptoms that I am seeing.

When I start my car, the engine sounds fine until I shift out of park and into any other gear. Once out of park, the engine begins to rev as if I were tapping the gas pedal repeatedly in 1-2 sec intervals. This will continue for about a minute or two, or until I shift back into park and press on the gas pedal for a few seconds. Also, this only happens after my car has been sitting for more than a few hours (over night or parked at work all day).

Today I decided to open the hood, start the car, shift to reverse and back to park (so the engine would repeat the symptom), and listen to the engine a little closer. I noticed something that sounded like a struggling pump, possibly coming from the vacuum pump. But this is only confusing me more because I replaced the vacuum pump less than a year ago because the old one was leaking.

Does anyone have any insight into what the issue may be? Or has anyone had a similar issue? I'm going to take the air pump off this weekend and poke around a little more, but if anyone can make a recommendation as to something else that may be causing this issue, I would greatly appreciate your input.

Thank you.

brettysetgo

Common problem on our cars. My car has had P0140 for years and I'm still trying to figure it out. My car also does not have the jet engine sound. It's not the fuse, the pump appears to be working. Your C300 revving sounds like it could be a completely different problem than the Secondary Air Injection system - maybe a computer error? It'd be worth taking into an indy shop that has the Mercedes-Benz diagnostic tool to get a deeper read on it.

In regards to fixing it yourself - check out these videos, go through them and see if they can help you at all. And report back with the results, because I'm pulling out my hair trying to figure my P0140 as well.

Steve_Kaboom

After weeks of searching and discussing the issue with friends, mechanics, and Mercedes, I've come to the conclusion that there must be little gremlins hiding in my engine, playing tricks on me. Because the problem seems to have just disappeared.

I've had a full diagnostic run twice, with multiple codes coming up. The first time I was told it was relating to the mass air flow sensor, so I replaced it. The second time I was told that all they could find was an air hose that was detached, and that they reattached it (which did not fix the problem). I even took it back a third time (to Firestone all three times) and asked them to look at it without running it through the computer. The mechanics said that the issue was probably related to the intake manifold. That'll be about $1000 just in parts. And both a mechanic friend and a tech at Mercedes agreed that it very likely that that could be the cause of the problem.

I've been waiting all week for the engine light to come back on so that I could take it to Mercedes to have them diagnose it and confirm the source of the problem before I buy such an expensive part. But now everything seems fine. No revving, no jerking, shes a little sluggish still but otherwise fine and still no engine code.

I know this may be less than helpful, but I wanted to post an update. If the gremlins return and I discover the source of the problem, I will make another post. But for now, I'm at a loss.