testarossa idle problem

I have a 91 Testarossa with 27,000 miles I bought about 5 months ago. Today I drove it in a local parade for about an hour. About half way through when at idle my engine would would go up and down as if I were pressing and releasing the gas pedal. About 800 rpm to 1500 rpm. The car didn't over heat according to the guages. It quit doing it a couple of times but then after only a minute or two it started up again. Any one have any ideas? After leaving the parade and driving home at freeway speeds for about 10 miles it's still doing it. Also if anyone knows a good mechanic in the San Joaquin valley(Central California, Modesto) I would appreciate their name. Thanks Alot.....Charlie

 

Thanks to everyone for helping. I had read earlier post about the floor mat problem so when my problem started that's the first thing I checked. Mat was not near pedal. I just went and drove again and everything seems fine. The problem was intermitent originally, hopefully it's gone now. I don't understand how if the mat is on the pedal, RPM would go up and down. I would think RPM would go up, but be steady, I don't know. Any way the problem is gone for the moment. If it returns I'll post another request for help. Still would like to find a mechanic near Modesto California. Thanks again.....Charlie