I have a '91 300CE Coupe, M104 motor, and I have been dealing with poor gas mileage issues for some time. I had replaced the EHA valve a while back and fooled with the mixture some, but the EHA started leaking (used one). Replaced it yesterday with a brand new one and now I'm having problems. Two observations: 1) this car has always run better when cold. 31 degrees here today and it starts great, accelerates smoothly, lots of power, no hesitation - feels like a new car. But, as it gets warm, it's starts and stalls, idles rougher, get's sluggish, etc.

2) With the new EHA valve in, I adjusted the mixture to right around 50% - but when I get it to 2500rpm, the mixture jumps all the way to 14-18% - runs very rich to where you can really smell it. I am assuming this is contributing to my poor mileage. Why is it doing this? New O2 sensor just installed as well...Any thoughts?

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE