1999 Mazda Protege Stalling in Hot Weather

I have a 1999 Mazda Protege.

My wife was driving it a few days ago in hot weather and it kept stalling on the interstate. She would have to wait about 1-2 minutes before it would start again.

I drove it to a shop about 10 miles away where I usually have it serviced. On the interstate I kept it around 2,600 RPMs and it didn't stall. When I got to the bottom of the off ramp it stalled when the RPM's dropped to around 1,100. I waited about 1 minute and it started again.

Between the off ramp and the shop (about 1 mile) it stalled 2-3 more times in traffic when the idle spead dropped to around 1,100 again. Each time after about 1 minute I could restart it.

When it stalled the dash lights would flicker and the speedometer would bounce around 80-90 MPH even though I was stopped. It kind of sounded like the starter was clicking maybe (not sure of this). The speedometer and dash lights wouldn't stop flickering until I turned the ignition off.

The mechanic at the shop has driven it on and off for the past 3 days and can't duplicate the problem. Then again it hasn't been as hot out.

Does anyone have an idea of what could be worng?

I was thinking maybe the ignition coils are going.

Thank you.