Extreme exhaust restriction?

[Heep]

Hi again!

In my quest to get a neglected '89 300E running properly again, I replaced injectors 2 and 5 last night. Those plugs had powdery black deposits on them while the rest were fine. I had replaced those plugs prior to replacing the injectors, and while the idle did improve over what it was with the fouled plugs, it still wasn't right. The PO said those two plugs would keep fouling on him after driving it for a bit. Injectors were suspect though not definitely the cause - however, they're relatively cheap and easy to replace, so I figured I'd give them a try.

Anyways, that's my preamble...

I replaced the injectors last night and when I started it up, it purred beautifully - much better than I've ever had it running. I did notice, however, some exhaust gases escaping in the engine bay that I'd not seen before. Couldn't identify the exact source. Left the engine idling as I put my tools away, moved my wife's car, etc. As it was starting to warm up I noticed the exhaust leak was no longer visible, and the idle was slightly beginning to suffer. Vacuum gauge was slowly heading towards the red.

Went for a brief drive, and the car was bogging and chugging and lacking power - getting worse and worse the further I went. Barely got it back to the house. When I did, I opened the hood and saw one of the pre-cats(?? Bulbous canister thing right after the exhaust manifold) glowing orange, though the coolant was only up to 65 or so. Engine barely ran, was very reluctant to rev in park. Haven't had a chance to try it again from cold yet.

Could this be indicative of a major exhaust restriction? Could replacing the injectors have caused a change in the A/F ratio enough to exacerbate a problem with the exhaust?

Thanks,
Mark