300e idles smooth, then "coughs"
 

Hello Board, I have and 87 300E(146k miles). It recently had a "new"(89k miles) engine installed into it (form an 89 300e). I have done the plugs,wires,cap and rotor,voltage regulator and it seems fine. The one problem is that it idles fine, and then it sort of coughs. The exhaust also smells of raw gas,my gas mileage is bad(about 10-12 mpg). The car also has bad cold and hot strat problems, Is my cooland temp sensor at fault?, if so, where is it located on the 89 engine? any other suggestions to what can be causing these problems?

please help!

Raw gas out the exhaust indicates a extremely rich condition, scope the O2 sensor to begin with, or just replace it. Check the timimg.