About 2 yrs ago, in the winter, my car would occasionally stall at a stop light 1/2 mile from my house (cold start after sitting overnight). Maybe 2 days in a row then nothing for a month or 2. This winter it happened again at the second stop light - about 1 mile from home. Again, maybe 2 days in a row and not again for a month or two. About 2 months ago, this same sort of stalling started happening only after sustained highway driving - as soon as I come to a stop after exiting the highway, the rpms start fluttering and, if I don’t give it a little gas, it will stall. Starts right up but it will do this for about 5-10 minutes but only when I’m at a dead stop. No problems with sustained speed of 40 and under. No problems after the first 5-10 minutes after exiting the highway. Other than this, the idle is incredibly smooth. I put in new Bosch plugs 6 months ago. I replaced the wires 5 yrs ago with OEM wires from Toyota. I tried a new coolant temp sending unit - no luck. Someone on another web site I posted on said “same thing happened to me - I changed the wires and problem solved”. I’d try this but 1.) I’ve seen the old “same thing happened to me…” too many times and 2.) I can’t figure why wires would cause this problem. I’m guessing that sustained highway driving is heating something up and coming off the highway reduces the cooling effect of rushing air. Any ideas???
[b]The problem might be with the Idle Air Bypass motor.
The IAB motor controls the engine idle speed anytime the accelerator is released. This is basically a stepper motor that moves to various positions to allow idle air into the engine past the closed throttle plate.
These motors can become sensitive to temperature where they no longer move to the proper position for the idle condition. This can result where the engine idle speed goes out of control, or where the engine stalls anytime the accelerator is released.
This isn’t directly related to your problem, but I would definitely exchange the Bosch plugs for NGK.