Not run correctly

Use a vacuum gauge to check for a plugged cat.

Testing for blocked exhaust

"Starting with the engine at idle, slowly increase engine speed to 3,000 RPM, engine vacuum should be equal to or higher than idle vacuum at 3,000 RPM. If vacuum decreases at higher engine RPM's, an excessive exhaust back pressure is probably present.

Idle speed reading slowly dropping toward zero indicates exhaust restriction.

Excessive backpressure in exhaust then indicated by reading not increasing quickly to about 16 in Hg

when engine speed slowly increased to 2000 rpm.
Backpressure also indicated by reading not dropping as quickly when throttle quickly released and remaining 5 inHg higher or more than normal."

If that is not a problem check the map sensor. Be sure the electrical connection is clean and tight. Be sure there is vacuum to the sensor. Check for goo in the vacuum line at the sensor.

Good luck and let us know. :)