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TSB 18-07-98

Effects of Incorrect Idle Speed

Visit Geno's Garage
for Truck accessories.

Date: Feb 27, 1998

Models: 1994-98 BR/BE Ram with 12 valve Cummins

Notes:

Several strange things can happen if the 12 valve Cummins idle speed is too high or too low. Incorrect idle adjustment may cause different customer concerns - low and high idle problems can and should be corrected.

RPM BELOW SPECIFICATION

Hard starting/stalling during cold engine operation.
Engine roughness at idle.
Reduction in vacuum available from vacuum pump during idle.
Delayed power steering assist when cold.
Excessive seat shake and/or mirror vibration.

RPM ABOVE SPECIFICATION

Excessive creep at stoplights/signs.
Vehicle does not reduce speed with foot off throttle.

Typical low idle speed is caused by misadjusted low idle speed screw on the injector pump but high idle speed can be caused by many items. The following list will help in diagnosing high idle concerns.

CAUSE	REPAIR
Idle speed misadjusted	Adjust low idle screw on injector pump
Misadjusted throttle/cruise control cable	Adjust cables
Throttle linkage rod binding	Clean and lubricate ball connections
Bent throttle rod	Replace rod
Broken return springs	Replace springs
Throttle/cruise cable damaged	Replace cable

Correct speed is:
1994-1998 with AT - in drive with AC on 750 -800 RPM
1994-1998 with manual in neutral with AC on 750-800

Use DRB III or an optical tach such as Cummins #3377462 or Snap On MT139 or equals must be used. DO NOT USE THE INSTRUMENT PANEL TACH FOR SETTING OF IDLE SPEED.

Policy: Information only.

Thanks to Bob Bergevin for providing this TSB information

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This page was edited on: May 3, 2004