Engine starts and runs fine at idle, but under light (6/7 lbs) boost, engine starts to stumble and black smoke is present. Gets worse in 3rd and 4th gears under boost. Runs fine in all gears without any boost being applied. Checked codes and only receiving a 12 code. Recently performed some basic spring cleaning, hoses, spark plugs etc. Check all hoses, plug wire and vacuum lines appear to be tight. All sensors are connected and seated properly. I do not have a scan tool to use. Any thoughts or suggestions on what might be causing the problem would be appreciated!
Two thoughts / suggestions:
#1 - How did it run before you worked on it, better or worse? If better, then it is likely something you did, or didn't do, during the spring cleaning. Go back and closely double check your work. If the car ran worse before you worked on it, see #2.
#2 - Bite the bullet and get a scan tool. A data recorder (like TL or DS) is best, but if you don't have access to a laptop, a scan tool will do you just fine. I'm partial to the SM. Without something to look at sensor data, even though all the sensors may appear to be connected and seated properly, they may not be. Also, you don't know if the sensor ist functioning. A scan tool of some sort is a necessity with a TR.
Dean