Runs Rough when Warm

[courtenay]

My '80 Fi starts great and runs strong for about a half an hour. Then it starts to run really rough when I stop at a light etc. Major hesitation and has even stalled a couple of times. Restarts and kicks a bit, but once back up to speed, it seems OK - until I stop again. I have checked for vacuum air leaks, and everything appears to be fine in that regard.
Any suggestions as to where else to look would be appreciated.

[RRoller123]

There are a bunch of possibilities, but check to see if the charcoal canister is blocked. Pull the top cap/plug and make sure there is vacuum when idling, there will/should be as it connects directly with the intake manifold. The injectors may be old and leaking when they warm up, or the reverse, One can listen to them click with a stethoscope, although that won't reveal if they are actually passing fuel properly. CSI may be leaking when warm, make sure that the TPS is properly adjusted. Check that fuel cap is properly sealed, if so, the charcoal canister is the only way that make up air gets back into the fuel tank. Just a few suggestions. Probably related to heat?

[Odoyle]

Could be a multitude of things, I was having intermittent starting issues last year only when car was hot. Turns out it was a bad magnetic pickup module who's resistance reading changed as engine got hot, misdiagnosed and replaced, check valve, vapor separator and vapor canister. Don't feel too bad throwing new parts at 40 y/o car tho.