I had the opposite problem.........that is mixture a bit too lean when engine was cold. Ironically the problem shows up during warm weather but not during winter. I replaced the coolant temp sensor which helped a bit and then spliced a variable potentiometer ( I seem to remember using a 5K ohm) in series with the coolant temp sensor. Dialing in a bit richer mix at startup smooths out idle; no stalling and after a couple of minutes running, dial the potentiometer back to zero resistance. To add acccuracy, I installed a generic oxygen sensor in the exhaust pipe just below where its connected to the exhaust manifold. This feeds an air/fuel ratio gauge. Good luck