Starts Misfiring When Warm

[RRoller123]

Odd problem, wonder if any of you have any thoughts or similar experience with this. My 80 FI Spider 2000 runs fine for about 40 minutes, then I experience some misfiring. I will be moving along steadily at say 3000rpm, and the engine starts to skip a few beats like it wants to die. I punch the gas and it recovers with plenty of power. It only does this after quite a while of driving. Once it cools down, it is fine and the cycle is repeated.

I read somewhere here that a faulty fuel pump may get noisy near the end of its life. I can hear mine clearly when the ignition is on (before starting), not sure if this is normal or an issue. I was thinking maybe the FP is binding up as it heats up (?) I also ordered a new ignition control module (under the coil), and I have a new vented gas cap. Plugs are new, coil resistance values are fine. Coil wiring refurbished. Spark Plug wires are fine. Any thoughts on what can cause this? Thanks in advance for any ideas. The problem keeps me around town, I would venture further afield but don't want to get stranded.

Pete

[So Cal Mark]

might be too lean

[aj81spider]

I had a similar problem. My 81 FI would surge and drop power briefly after the car was running for a half hour or more. Not sure yours is the same, but mine turned out to be a cracked air hose between the AFM and the intake. I found this out by accident when changing the plugs and pulled the hose off for better access. That would also match Mark's diagnosis of too lean (air getting into the system around the AFM).

[RRoller123]

Thanks for the responses, I will check that out. I have made sure the connections are tight, but there could be a break somewhere. I suppose also that the aux air valve could be faulty and letting air in?