Author Topic: Vibration/Rough Idle  (Read 1311 times)

Offline Lifted1

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Vibration/Rough Idle
« 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?

Online bd

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Re: Vibration/Rough Idle
« Reply #1 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 and follow the diagnostic tree for Code 13.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JohnnyPopper

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Re: Vibration/Rough Idle
« Reply #2 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.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Stewart G Griffin

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Re: Vibration/Rough Idle
« Reply #3 on: July 25, 2019, 10:10:02 PM »
Is this a California truck?