Rough Idle. What do I replace next?

Asked by Aug 25, 2017 at 01:08 PM about the 1998 GMC Sierra 2500 2 Dr K2500 SLT 4WD Extended Cab LB HD

Question type: Maintenance & Repair

My Sierra 2500 (manual transmission, 180,000 miles, 5.7 liter, extended cab,
4x4) went from 15 mpg to 10 mpg suddenly. I've replaced spark plugs, spark
plug wires (they were worn), the ignition switch, fuel filter, fuel pump, ICM
(because it was cheap), and air filter. It still idles poorly. It starts great and
runs well, but idles poorly...and poor mpg. What's next? Should I be looking
at the fuel regulator?

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