PeachParts Mercedes-Benz Forum - View Single Post

DAVID LEE · #24 03-26-2008, 01:31 PM

Hey Glyn:

I hope you don't mind someone else jumping in here, but your thread reminds me a lot of my 1st few weeks of 300E ownership about 7 years ago. I had some similar issues as you, and in particular - the "sudden fast idle" issue.

I hit upon my solution after reading one of Steve Brotherton's articles and so I'm going to suggest that you may possibly have the same issue I had, and that the fix might be the same as well. As you know the ECU gets feedback from a number of sources, and one of the sources is the temp-sensor at the very back of the head. As you stated earlier, there are two sensors - one for the temp gauge and one for the ECU. Not sure why it takes two. Anyway, the sensor would "intermittently fail" and then "un-fail" resulting in the exact phenomenon you mention - erratic fast idle. It's pretty easy to check the resistance on the sensor, but when it is intermittenly failing it is rather difficult to pin it down. The sensor only cost $20 USD (here in the states), so I simply replaced it (based on Steve's article) and the problem has not returned. Another idle issue I was having ended up being a clamp not being tightened on the hose coming out of (or into - I can't remember) to the idle air control valve - that thing you mentioned that is in front of the fuel distributor (I assume it exists on a Euro car). The idle might surge to around 900rpm and then return to normal 600rpm in a matter of seconds. Insuring all the hose clamps were tightened fixed that problem. The reason I bring it up is that it sounds like you may have removed it to "see what would happen".

Since the initial issues I had, the car has been one fantastic machine. I had a lot of "little" things to initially fix, and like you I thought there couldn't be one more thing that could "pop up", but eventually, the issues were resolved and I'm quite happy with the car. I get just around 20 mpg around town here in North Carolina, and I'm quite happy with that.

I'm somewhat puzzled by your accelaration issue and only have one thought. I've read over the years on this site about timing chains getting stretched to the point where the timing was actually retarded about 12 degrees. Someone else has eluded to that in one of the posts, so it might be something to think about, although on these 300's 100000miles is really not many miles and would normally be much too early to worry about a timing chain.

Hope you get things running to your satisfaction,

Dave