i have 91 civic with a d15b6, black smoke coming out of tailpipe and idles around 200-400. will not hold constant rpm when rev up engine. has trouble starting up unless pull vacuum hose out then begins to idle better, put hose back in and idles around 500. cannot figure out how to fix pos. any suggestions besides a match

 

Is the LED on the ECU blinking a trouble code(s)?

The black smoke indicates that the engine is running way too rich.

You might try cleaning the IACV and FITV for the low idle problem.

 

Could also be excessive fuel pressure making it rich. Is the vacuum hose on the back of the fuel pressure regulator hooked up properly?

 

i have had code 3 and code 5 blinking on the ecu. replaced the iacv valve couple weeks ago, but it never fixed the surging problem.

 

I think you have found the problem. Codes 3 and 5 indicate a problem not with the IACV but with the MAP sensor or its circuit. The three diagrams below tell you how to troubleshoot code 3:

 

Here's how to troubleshoot code 5: