Engine stumbles at city speeds

[iank1]

OK, '94 2.3l 5 speed stick, no AC with California emissions. So I have this glitchy problem. It only happens after the truck heats up and after a restart. I'm rolling along at about 40 and it's like someone takes ahold of the ignition circuit and flips it on and off about 10 times fast. If I roll up to a stop the engine holds at about 3500 RPMs untill I come to a complete halt, then drops to idle. usually there is a CEL light too. I've replaced everything, I mean EVERYTHING except the ECU. And yes, the ICM is well grounded. HHHEEEEEEELLLP!