A few years ago I had this crazy high idle that would have me zooming down the street at 30 mph without touching the throttle. I replaced the throttle body with a used one which remedied the problem.

Recently the problem has returned but it's not nearly as bad - it mostly just idles around 1,500 rpm for a few seconds after I come to a stop. I (supposedly) separately have a P0400 code that pre-dates the high idle by a few months.

I watched a rabbit-hole thread of videos on youtube trying to figure this out. I found a video where a tech used a shop glove over the MAF inlet (removed the engine cover) to test for a vacuum leak and then turned the engine over for a few seconds to pull a vacuum. If things are sealed, it should hold for many seconds. His held until he pulled the dipstick out. A side note: my dipstick doesn't seal inside the tube like his did (Mercedes M112).

When I did that, I had a big hissing sound around the throttle body/MAF and the vacuum dissipated within a few seconds. The MAF doesn't seem to be terribly solidly mounted on the elbow (yellow arrow below) to the throttle body which could be a source of the leak but I don't know if this is normal or not. And I don't know that this is where the hissing sound is coming from.

Any ideas?

Thanks.

 

If the sound is really coming from that junction, then it is obvious: the seal there is inadequate.
I'd fix that and see where things go from there.

 

I removed the MAF and cleaned the upper seal between the MAF and the elbow and the lower seal between the elbow and throttle body. They each looked to be in good shape. When I put it back together and retested, I got the same hissing sound. I should have been clear that the sound is coming from that area but I can't be sure where it's coming from. It could be coming from the MAF vent hose... or somewhere else. I could just start replacing seals and hoses until the problem is resolved.

 

I've used a piece of hose next to my ear before to narrow down the source of a sound.

 

I've tried to find the upper and lower MAF seals online but can't find one that I know will fit the Crossfire. So I contacted the local MB dealer who said there are four different ones listed for the 2003 SLK320 so without a VIN he wouldn't know which one to sell me. This doesn't make much sense to me since when shopping for MB parts online, they don't ask for the VIN. Of course, the Chrysler dealer doesn't have any information or parts.

I could just glide a thin coating of rtv around the seals and hope that I don't eff them up.

How are you guys finding NEW parts like this? After nearly 20 years of of ownership, it feels like it's time to unload this. But, after I fix it.

 

Have you tried asking needswings?

 

Thanks for the reminder! They hooked me up.