I thought I started a new thread, but I stuck this question on the end of an old one, so here we go again, shorter version. 99 5.9 won't idle right and starts breaking down at 3000 RPM. Was dumping raw gas through exhaust. Found one plug wire broken at plug. That would be the raw fuel. Replaced wires, plugs, cap and rotor. Runs better on all eight, but still not running well. Still won't idle more than a minute or so and it stalls out. Still breaking down at 3000 RPM. Replaced the Idle CV and MAP sensor. Has 135,000 miles. Runs very smooth from 750 to 2900, then starts popping and coughing. No codes, no CEL. What am I missing? Joe.

 

Bad gas, clogged cat, bad O2 sensor, (not real high on the list though.) or failing crank sensor.