Did you disconnect the battery to reset the learned fuel trims (also erases any stored codes in the ECM)? Remember the vacuum line to the fuel pressure regulator also is connected to the MAP sensor. If your MAP is disconnected it can really screw things up. Reset the ECM by disconnecting the battery then start fresh.

You do not have a significant vacuum leak (if any) if the engine dies immediately when you plug the IAC port. No worries there.

Any chance you cat it shot/clogged? That "may" cause rough idle... I do not think your top-end service would have damaged your cat. But it could just be a coincidence <sp?
Maybe temporarily disconnect your down pipe from y-pipe and see if the idle is smoother (will be very loud, do not run for extended lengths of time)...

[This message has been edited by ALJR (edited 06-24-2010).]

This is really very weird. I doubt the problem are the new injectors. You checked the basics for timing and if plugs are tan it is not pig rich. Tune or old learned will has no big effect as you are seeing. You said the distributor was not moved before and after new injectors nad before was running fine. It will not run with MAP disconnected. If it is runing that bad it sounds to me like it is running in limp mode. Maybe somehow your ECM went bad. Can you find one from a friend's Fiero to test? Also check all sensor connections. Did the brake boosted pipe is properly seated? That will cause leak but not rough running thou. Did you reconnected the injector wires (and banks) correctly? Not sure if banks may matter.

quote Originally posted by Hudini: Did you disconnect the battery to reset the learned fuel trims (also erases any stored codes in the ECM)? Remember the vacuum line to the fuel pressure regulator also is connected to the MAP sensor. If your MAP is disconnected it can really screw things up. Reset the ECM by disconnecting the battery then start fresh. You do not have a significant vacuum leak (if any) if the engine dies immediately when you plug the IAC port. No worries there.

I did try disconnecting the battery to reset the ECM. No significant change. I have verified that the MAP sensor was connected.

quote Any chance you cat it shot/clogged? That "may" cause rough idle... I do not think your top-end service would have damaged your cat. But it could just be a coincidence <sp? Maybe temporarily disconnect your down pipe from y-pipe and see if the idle is smoother (will be very loud, do not run for extended lengths of time)...

Will try taking the o2 sensor out..see how she does. thanks again for the suggestions

Just a tip: Check the TPS. My car was going rich with a bad smell. No errorcodes.
On idle the rpm was going up and down.
The scantool indicate a hi number on the TPS. I replace it and the problem was gone.
(sorry about my poor english).

Thanks to everyone who contributed to this thread.

I reassembled everything for a final time and the engine runs much better. Not perfect, still has a low rpm stumble, but doesn't feel like its missing a cylinder anymore.

The last things I did were: change the plug wires again, replace the throttle body gasket, upper plenum gaskets, and EGR tube gasket, reseating the fuel injectors and their connections, replacing distributor cap, and reseating the fuel injection fuses. It's frustrating, because I already did all of the above previously - maybe it was a combination of things.

FWIW, unplugging the cold start injector did not affect the running too much, just made it harder to start (but wasn't sticking). All of the cylinders ARE firing now (as confirmed by pulling plug wires). Pulling either injection fuse made the car run very poorly (but it did run, surprisingly).

I am going to change the TPS and check the MAP - thanks for the tip, Klausse.

Now I need to figure out why I have a low-rpm stumble, but I will start a new thread for that. Thanks again all.

[This message has been edited by masospaghetti (edited 06-28-2010).]

To follow up, the rebuilt injectors were faulty, a set of junkyard Multecs had the engine running smoothly again.