Engine - Rough Idle Cold or Hesitation
90chevy21Number: 90-163-6E
Section: 6E
Date: February 1990
Corp. Bulletin No.: 036501
Subject: ROUGH IDLE COLD/HESITATION
Model and Year: 1990 C, K, R, G, P, V TRUCKS WITH 7.4L (VIN CODE N) ENGINE
Owners of some 1990 C, K, R, V, G, P-trucks with a 7.4L engine may comment about rough idle cold or hesitation.
Either of these conditions may be the result of calibration and/or current starting procedure.
For trucks above 8500 lbs. GVW (not used on C-10 Chevy SS), a new calibration PROM is available. For correct usage see chart below.
NEW
NEW PROM BROADCAST NEW SCAN
TRANSMISSION KIT NUMBER CODE TOOL I.D.
3-Spd Auto (M-40) 16151512 AUMZ 1331
4-Spd Manual (M-20) 16151516 AUNA 1341
Parts are currently available from GMSPO.
For all 7.4L trucks (including C-10 Chevy SS), the starting procedure is as follows:
Existing Cold/Hot Engine
Do not depress the accelerator pedal. With your foot off the pedal, crank the engine for 3 seconds. If the engine does not start in 3 seconds, push the accelerator pedal to 1/4 throttle for the remainder of the 15 seconds. If the engine does not start, wait 15 seconds to let the starter cool down. Then crank the engine at wide-open throttle for a maximum of 10 seconds. If the engine still does not start, wait another 15 seconds and repeat the entire procedure. Release the key and accelerator pedal when the engine starts.
New 7.4L Cold Starting Procedure
At ambient temperatures of less than 60 degrees Fahrenheit, follow the procedure as outlined above, except depress and hold accelerator pedal 1/4 down for about 2 seconds after engine has started.
Use Labor Operation Number: T0500
Use Labor Time: .6 hr. for C/K/R/V/P models .7 hr. for G models