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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Lifted1 on July 24, 2019, 11:50:45 am

Title: Vibration/Rough Idle
Post by: Lifted1 on July 24, 2019, 11:50:45 am

Hello,

I am struggling with an issue with my 1983 GMC Sierra 5.7.  I recently replaced the fuel filter, spark plugs, plug wires, diz cap, rotor, O2 sensor, HEI module, most vaccuum lines, and i still cant get this thing idling smooth when hot.

thing is, when cold and first started it runs good. then as the choke is off it runs like a dog and wants to shake. if i give it gas it runs better so it seems worst at idle under load like at stop sign.

any ideas?  Im thinking of trying the coil next or pcv valve? i'm just throwing money at it now. i jumped the a/b obd1 terminal last night and there was a code 13 so i did the 02 sensor. which was dirty but made no difference.

any ideas?

Title: Re: Vibration/Rough Idle
Post by: bd on July 24, 2019, 12:47:40 pm

Throwing parts at the symptoms won't gain anything.  Verify the firing order then determine whether the engine is idling lean.  Using aerosol carburetor cleaner, spray around the carburetor and intake manifold to search out any vacuum leaks.  Temporarily pinch off the power brake booster vacuum hose to see if warm idle improves.  Once that's accomplished, use the 1983 Service Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_83_1983_Chevrolet_Light_Duty_Truck_10_to_30_Service_Manual.pdf#page=1059) and follow the diagnostic tree for Code 13.

Title: Re: Vibration/Rough Idle
Post by: JohnnyPopper on July 24, 2019, 05:59:37 pm

I agree with BD, sounds like a vacuum leak.

Does it have a EGR valve? Could be leaking.

Title: Re: Vibration/Rough Idle
Post by: Stewart G Griffin on July 25, 2019, 10:10:02 pm

Is this a California truck?