Not long ago, a mechanic tried to run diags on my '91 and came back and told me that he couldn't perform a 'running test'. What is this and what could possibly cause it. As an FYI, the problems my car experiences are as follows: idle surge, stalling, and running rich (I get 15MPG REGARDLESS of how I drive when I used to get 27MPG highway, this started before the mods began). I understand that my car can probably use a tune since modding, but my problems started before the mods. Heh, I add a cam and #24 injectors, and still get the same mileage. O2's, IAC, coolant temp sensor, etc. have been replaced. This is a good one.