2015 Tahoe P0300 Random Misfire and Stuttering at Idle

Question

My Tahoe started shaking pretty bad at stoplights and the check engine light is flashing periodically. It seems to smooth out a bit once I get up to highway speeds, but the idle is very rough and it feels like it's down on power when merging.

Megan Rivera · Accepted Answer

Found the issue; it was a massive vacuum leak at the intake manifold. I replaced the intake manifold gaskets (Part #12626354) and also discovered the brake booster vacuum line had a hairline crack near the check valve. Total cost for the gasket set was about $45 and it took me 3 hours to swap them out and torque the manifold bolts to 89 lb-in. The idle is perfectly smooth now and all codes stayed cleared after a 50-mile drive.

Lina Brooks · Answer

Since you have P0171 and P0174 lean codes along with the misfire, you should check for a vacuum leak. These 5.3 engines are known for the intake manifold gaskets leaking or a cracked PCV hose.

hd_trucker_77 · Answer

Check your fuel trims using a scan tool. If the trims are high at idle but drop when you increase the RPMs to 2500, you definitely have a vacuum leak behind the throttle body.

Pete Sanders · Answer

I would inspect the fuel injectors on these direct injection motors. Sometimes a clogged injector can cause a lean condition that triggers a random misfire across the bank.

2015 Tahoe P0300 Random Misfire and Stuttering at Idle

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