I just changed the heater core in my 94 Tercel. Everything seemed to be good for the first minute, then the engine started running rough. It dies frequently on idle, and seems to be generating exhaust fumes (some smoke). What did I do, or didn't do? Seems like my work had nothing to do with the engine. Could I have damaged the EFI when I connected the new battery? Is the EFI on a fuse? This is the only area that I could possibly have impacted. Any help would be greatly appreciated!

I am basically having the same problem with my 94 tercel too....I have changed almost everything in my car and now it seems to be dying when it's at an idel??? I took it to the shop like 10 times and they said it was the TPS (throttle Positioning Sensor) but I replaced that and I am still having the same problem....Do you think it might be the ECM???? Just wondering if theres someone that can help me out....THANK YOU!!!

My issue turned out to be a vacuum line to the MAP sensor. I probably popped it inadvertently when I was tugging on the speedometer cable inside the car. Hope you find your problem soon!

I found this on another forum from a guy who pretty-much fixed his similar problem...

"seafoam is an engine additive to clean all the gunk and carbon out of your engine.....get your car up to temp....unplug your hose from the pvc idle her up to like 2000 and let the hose suck the seafoam up through your engine....it'll smoke like hell...when the seafoam is almost gone..let your engine stall out by flooding it with seafoam....let sit 15 minutes....go and start her back up...go out and drive the crap out of it....it will smoke bad for 10 - 15 minutes......improvred my throttle response...idle...and mpg....awesome stufff.....ayrozone hasit and so does oreilly"