1995 Mazda 626 Power Loss at Low RPMs, bad idle

Engine problem
1995 Mazda 626 6 cyl Wheel Drive Type unknown Manual 160000 miles

My Mazda 626 is a V6 manual, it has run fairly well since purchased with recent repairs made for the timing belt. When just started and cold, it runs well and keeps a high idle speed. After the engine warms up and the idle speed lowers, the rpms dip down and shutters while idling. During acceleration, between about 2k and 3k RPM, there's lurching and jerkiness, with a power loss, then at 3k, there's a big burst of acceleration and the car runs full steam ahead. So long as the rpms are above 3k, or I'm just cruising at a steady speed, it runs fine. I checked the air filter and it looks brand new; probably replaced when the timing belt went out. Also, the check engine light came on intermittently after an hour or more of highway driving, but was running just fine at highway speeds until trying to accelerate up hills, then there was significant power loss.