Hi guys, this is my first post here and I could use some help.
I recently purchased an 89 RS with 305 TBI and 5 spd. Just before I bought the car it had plugs, fuel filter, air filter and fluids replaced. During the test drive the car of course ran great... until about 3 miles from home. She got a nasty misfire at part throttle which then developed into lots of bucking, a major loss of power and very strong fuel odor. I barely managed to limp the car home and could only maintain about 5 mph. Oddly enough the idle remained smooth and steady at 750.
The next day I checked codes and got code 23, MAT sensor, so I changed that out along with replacing several rotted vacuum lines and made sure all my electrical connections were clean and tight. The temperature never came up above 150ish either (even with the electric fan not working, another problem for another post). So I also replaced the 160 deg thermostat with a 195, I have to get this thing thru California smog, and now operating temperature is much more normal.
Heres the problem: When the car is cold it takes a good 5 seconds of cranking to start and then she seems to run fine, after warming up I get a misfire in the 1750 - 2000 rpm range. Shifting gears clears it up until I reach those rpms again. Hot starts are fine and there are no codes other than 12.
Ive only got a few more days to get this things smogged and I dont want to waste money by taking the car in while its not running right or frantically replacing random parts. Im going outside to check the spark plug gaps and rule out some more dumb stuff, any advice on where to check next would be greatly appreciated.
Thanks for reading my novel guys, great website here!

 

Check the plug wires, make sure they are on tightly.
Check continuity on each wire - new wires are often bad.
Check firing order to make sure that the PO didn't screw it up.
Check timing - unplug the EST wire first, and adjust if necessary according to the sticker under the hood (I thin it's to be set at 0* BTDC.

 

what engine?

 

My first guess was a clogged converter, but that wouldn't affect the cold start condition. I'm wondering about the fuel pump, really messes up engine operation when fuel pressure is low.

 

Thanks for the suggestions guys, it turned out to be a toasted distributor and a bad spark plug cable. Still have the cold start issue and kinda sluggish pulling thru 1st and 2nd, but then again it is a 170 hp boat anchor 305. Anyhow, drive ability is greatly improved, now its smog shop time and then upgrades!