Engine Performance problem
1997 Chevy Cheyenne V8 Four Wheel Drive Automatic 248000 miles
My 1997 Chevy P/U looses power under load, like when I'm accelerating or climbing a hill. The problem first started when I replaced the vacuum idle motor. I've replaced the fuel and air filters. When it looses power the max speed I can get is 15mph. Putting it into neutral, the max rpm is 3000. When the vehicle is working right, the rpms will go to at least 5000. Help.
Check the catalytic converter for a broken bed material. If you have a vacuum gauge, attach it to manifold vacuum, raise the idle to 2000 rpm, if the needle starts to drop, the exhaust is plugged, pieces of broken converter can lodge downstream in the pipes and mufflers, and intermittently move, allowing exhaust to flow. As it shakes loose, it allows the exhaust to flow enough to drive it.