Engine Performance problem
1991 Mazda 929 6 cyl Two Wheel Drive Automatic 49,587 miles
At start up - (cold start, i.E, below normal operating temp - not dependent on ambient temp.) At colder ambient temp. (Say about 40 degrees) engine will usually run at 2000 to 2400 RPM and stay at that speed until reaching operating temp. Will not kick down until operating temp. Even when acelerator is pumped several times. At normal operating temp idle is 650 and runs fine. At higher ambient temp. (Say 70 degrees) engine will start, run at 2000+ for a short while, then surge between 1200 and 2400 RPM. Continues erratic surge off and on until operating temp. Reached - then idle is normal 650 RPM and runs fine. Additionally, check engine light comes on after normal operating temp. Is reached and fuel economy is poor (12 to 13 mpg). Sounds like choke problem, but I am unsure of which component controls and where it is located. Reapir or replace? Low mileage car 49,500 actual miles - older preson's car and not driven much.