1988 T10 Blazer, 4.3, stalling when warm.

The '99 Blazer is in the shop, so I'm driving the '88 until that's fixed. 4.3 V6, 4wd. 191K miles. Now beginning to have a problem with stalling.

At first this was when I started driving (i.e. cold engine), but no code set. Finally after some days the Check Engine light went on. Checked the code, was for MAP sensor and EGR. Thus far replaced the MAP sensor, also the hose to the EGR valve was collapsed in the middle so replaced that as well.

Now car runs OK when cold, does fine at highway speed, but then if I drive on the highway for an hour or so, it stalls at the first traffic light I get to after coming off the highway, if I keep it in Drive with my foot on the brake. Then runs rough after restarting. If I coast in Neutral up to the light, the idle speed goes right up to 1500rpm (by itself, I'm not reving it up), and eventually it drops back to 500 or so and then stalls, unless I keep tapping the gas to keep the idle speed up.

When the car is by the mechanic it works fine, I think it's afraid of him.

Where do I go from here?

Shalom S.