I have recently replaced my engine in my 1988 300CE with a used one that had about 65k miles on it(That' what the owner said anyway). This engine idles rough when in traffic. Took the car to the dealer and they said that I had to replace the valve seals because it was letting oil in the #6 cyl. Hence the fact that every 200 miles it needed 1 quart of oil. The seals were replaced and it gave a "much better oil consumption". When I get stuck in traffic though it still does the same thing. Unless I drive it on a long stretch e.g freeway to get rid of all the carbon or oil deposits, it just doesn't work right. You do that and then it's fine until I let it idle again. Any ideas???
I also need to know where the cruise conrol amplifier and relay are located for replacement. Is this a DIY thing if I have the replacement parts?

Thanks.