After you have checked for loose air intake fittings and/or vacume leaks--
The most common problem is a dirty/fouled air flow sensor that is sending a false signal. It is mounted on the air cleaner housing and secured by two screws.
Unplug the wiring harness, and then remove the sensor. I have had some success cleaning the sensor with brake clean and then lighty blowing it off with compressed air.
If all else fails, do it right and install a new sensor
After market, open element air cleaners are know for causing problems with the air flow sensor.
1980 Toyota - 1997 3RZ-FE 2.7l Engine, Turbo R151F 4.31:1, Triple Turbo Marlin Crawler Billet (2.28x4.70x4.70) = 1,148:1 Crawl Ratio, Marlin Crawler Twin Stick and Short Throw Shift Kits, 30mm H/D Output Shaft, High Angle Drive Lines, 5.29:1, ARBs, High Pinion Front, 25mm HD Billet High Steer Kit, 6 Pin Locking Hub Bodies, 86+ Wide Rear End, V6 3rd member, Chromolly Axles all around, 37" IROKs with Beadlocks, York onboard air - Rollbar air tank, Premier Power Welder, Marlin Crawler 4" USA-made Leaf Springs, Bilstein Shocks, et cetera....