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1998 Pontiac Transport P0300 Misfire: Short-Start Issue After First Startup

Model: 1998 Pontiac Transport Fault Code: P0300 Posted: 2015-05-25 00:25

My 1998 Pontiac Transport (166,000 miles) exhibits a recurring engine misfire with fault code P0300. The issue only occurs during the first startup of the day—after initial ignition, the engine misfires for about one minute before running smoothly. Subsequent starts on the same day are unaffected. The Service Engine Light activates briefly and then turns off. I live in Southern California with temperatures typically above 60°F. I’ve already replaced both the crankshaft position sensor and camshaft position sensor, but the problem persists. The car passed a California smog test on October 27, 2014, and has not shown any changes in fuel economy—MPG remains consistent. I only drive approximately 50 miles per week, mostly short trips with no highway driving since summer 2014. I’ve considered whether the issue is related to fuel system pressure or electrical components. Could it be that the fuel system loses pressure overnight, leading to poor performance on first startup? Does turning the ignition on (without starting) activate the fuel pump and pressurize the system? I’m looking for cost-effective solutions—such as a fuel pressure test and a pressure leak-down test under KOEO conditions—and am considering whether adding a fuel cleaner like Techron would help. I currently use Chevron gas, which contains Techron. Does this still apply? How often should it be added?

Related fault codes
P0300
Comments (6)
Anonymous 2015-05-25 08:07

Perform a fuel pressure test and conduct a pressure leak-down test under KOEO (Key On, Engine Off) conditions to check for leaking injectors or a faulty fuel regulator.

Anonymous 2015-05-25 10:38

Thanks for the response—what does 'KOEO' mean?

Anonymous 2015-05-25 11:56

KOEO stands for Key On, Engine Off. This test helps identify fuel leaks or regulator issues by checking system pressure when the engine is not running.

Anonymous 2015-05-26 22:35

I don’t have a fuel pressure gauge. Before starting the car each morning, I turn on the ignition (key on) for about 30 seconds before attempting to start it. This significantly reduces misfiring and eliminates the Service Engine Light. Does the fuel system normally retain pressure overnight? Does turning on the ignition activate the fuel pump and pressurize the system? Could a discharged capacitor or electrical component be causing the issue during first startup? I only drive locally, so I’m trying to avoid expensive repairs like new injectors. The car has not been driven at highway speeds since 2014.

Anonymous 2015-05-27 07:34

Your description supports a fuel system pressure issue—try both the fuel pressure test and KOEO leak-down test. Yes, the fuel system typically holds pressure overnight. Yes, key-on wait before starting activates the fuel pump and pressurizes the system. No, the capacitor theory is unlikely—the first startup is inherently more demanding. No highway driving? Consider adding a bottle of Techron or Seafoam fuel cleaner to help clean injectors.

Anonymous 2015-05-27 23:06

Next step: I’m willing to perform a one-minute KOEO test for the first startup. No smell of gas was detected during this period—when I raised the hood and stayed outside, even though I didn’t see any fuel leaks. I’ve never noticed a fuel odor before, and once checked battery voltage with a voltmeter while the engine was off. Where could fuel be leaking to overnight? The morning start today was smooth—minimal misfire, no Service Engine Light. Given my limited driving (only local trips), I’m avoiding costly repairs like new injectors. I use Chevron gas, which contains Techron. Should I still add a bottle of Techron? How often is that recommended?