We just replaced the tranny and installed SLP headers in my buddy's 89 Formula 350. (no air injection, smog or cats) The car ran flawless before the swap. It will idle fine, but if you give it any more than a little throttle, it starts cutting out and running very rough, making no power whatsoever. We replaced the cap, rotor, plug wires, plugs at the same time. The car is stock except for the exhaust mods. His exhaust manifold was cracked previously and showed that it was running lean (not sure what the code # was, related to the O2 sensor). It still has that code showing now. Oh, and one time while it was idling, the idle speed jumped way up over 2000rpm out of nowhere, then settled back down to a normal idle. Any suggestions? Sorry about the long post.

I did find out that it posted codes 13 and 33. He put a new MAF and he said it runs better, but not very smooth. Thanks

 

Did you install a new 02 sensor when you put the headers in? If not, you probably need to.