My 1989 Formula Convertible is sick. The car has a 305 TPI, a 5-speed and dual cats. It starts fine, but usually idles a bit rough. It also feels a weak, has a stumble at steady throttle and spits black soot out of its tailpipe. The car is essentially stock and has 62,000 miles on it. It obviously sits more than I drive it. Have my injectors gotten old? Any help would be greatly appreciated.

you have multec injectors in that engine. they are all failing due to the ethonol in the fuel go to this and watch the videos\
http://forums.corvetteforum.com/show....php?t=2104010

I don't believe that 89 cars had multec inj.
blocker,maybe check your IAC.
BTW thanks for the link to the FIC vids!

I'm new to TPI, but I think 89 was the first year for Multec injectors. Didn't GM use Multec's until the end of TPI?
My car has Multec's from the factory. Not for long though. Jon sent new Bosch III's, and those Multec's are hitting the trash can ASAP.

Your problems sound like they could definately be caused by bad injectors. I think you need to do a tune-up (plugs, wires, cap, rotor, filters, etc.) first if this stuff hasn't already been done. Then check your fuel pressure. 43 psi line off. Check your timing with a light. A vacuum leak will cause your computer to do VERY funny things. Check for leaks around gasket areas. I had symptoms like yours on a TBI 350. The truck would occasionally puff black smoke, and it always ran a little rich. I had detonation at times, and sparatic driveability issues that I couldn't figure out for about 2 years. I found the throttle body gasket had a large section broken off, and it was letting lots of air in. You could see how the incoming air had erroded the broken edges of the gasket, and made them round and smooth. So, check those gaskets.

Now you have a good starting point if nothing else. All this stuff is necessary anyway, so don't look at it as a waste.

By the way, I don't think the IAC is going to cause weak performance, soot and stumbles while driving.

my 89 had mulittek's and they short out. the coil resistance drops down.