1998 S10 knocks and rough idle at start

1998 ALL OTHER MAKES ALL OTHER MODELS
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S10
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I have a Vortec 4.3 that knocks and idles roughly when I start it, especially on cold mornings or after it sits for a while. The knock seems loudest over cylinder 1. I ran engine cleaner (Gunk) through it once and it seemed to solve the problem. The knocking returned 1000 miles later. Put Gunk in a second time, changed the oil, and is silenced the noise until about 750 miles on the new oil. The engine has 76K miles on it. What is going on and about how much would it cost to fix it?
Jan 18, 2006 at 6:52 AM

What to check next

Diagnostic guidance. Suggested checks and possible repairs are separate from the owner's reported results.

Did the shop provide written diagnostic findings or an invoice stating which lifters were affected and what action was taken? Please share any shop documentation or exact wording of their diagnosis.

Guidance references and applicability

Source: Original question and visible replies. Owner reports and other participants' experiences are distinguished. Next steps are editorial requests for clarification or existing diagnostic findings, not a verified repair procedure or an independently confirmed component diagnosis.

Read the replies · Discussion summary and reported outcome

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AVALANCHE1
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i have the same problem with my 5.3 lit avalanche, took it in its still under warranty the told me it was carbon build up burning off and gave a written guarentee for 100,000 miles a few other friends have gotten the same thing
Jan 19, 2006 at 1:34 AM
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S10
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I just got a call from the shop. The lifters had lost their prime.
Jan 19, 2006 at 1:49 AM

Discussion summary

1998 S10 knocks and rough idle at start

1998 S10 with Vortec 4.3: owner reports a loud knock and rough idle at startup, worst when cold and loudest over cylinder 1. Engine cleaner (Gunk) temporarily stopped the noise once (returned ~1,000 miles later). Second treatment plus an oil change silenced it until ~750 miles. Engine has ~76K miles. Owner later reported the shop said the lifters had "lost their prime." A separate reply (different vehicle) suggested carbon buildup, but that is not the owner’s report.

Reported outcome: Owner reported the shop diagnosis that the lifters had lost prime. No repair completion or long‑term result was reported by the owner.

No shop report, invoice, or documented test results were provided. No confirmation which lifters or cylinders were inspected/repaired, what repairs (if any) were performed, or whether the diagnosis was verified after repair. The separate comment about carbon buildup is from a different vehicle and is unconfirmed for this truck.

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AI-ASSISTED SUMMARY · REVIEWED BY 2CARPROS
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