Fuel Injection Problems
There are many FI problems that can be hard to track down. This is one. My car was running very rough and rich. Plugs were black. Smelled "rich". I thought at first it was a faulty air meter. Switched one, no difference. A faulty TPS can cause derivability problems but can be checked easily by just unplugging it. I was think I would change plugs and look for signs of a blown head gasket... maybe two cylinders were connected due to missing piece of head gasket. I then tried to wiggle the coolant temp sensor plug. I know that a faulty coolant sensor will cause derivability problems but mine were severe. Well, turns out the plug connections were dirty. AS soon as I pushed on connection, cars engine smoothed right out.