Got an 8fgu18 63281 serial
Unit has 5000 hrs

Last week, customer contract for sputtering in pedal. Erratic idle. Presented as regulator issue. New regulator. Problem reappeared 2 days later. Evaluate. Have checked graphite inline filter. Main lock off opens as it should. Full voltage even when unit dies down. Slow path solenoid power and ground good. Throttle body side. Have found when issue occurs can remove air intake from throttle body neck and manually restrict the throttle body and unit will run as it should. No rhyme or reason for the unit to run smooth again but it will. Today, had the unit running at about 2000 rpm's for a period of 2 hours with no interruption due to issue. 40 minutes after I left, unit had issue return. Any ideas? No codes on the dash. Swapped tanks.