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Sometimes Slow Start & Come-and-Go PO420

  1. Slow Start has happened about twice a week, particularly when I drive somewhere, stop for under an hour, and try to start again. Normally it’d take three DIT DIT DITS and then it VROOMS (see? Car terms everyone knows.) On a bad day, though, it’ll happen 3-5x and have an unsettling lurch in the engine that I can feel more than hear, pausing for a second, then VROOM. That’s a real heart-stopper. WalMart checked the battery and said it’s fine: 500 out of 550 something and 12 out of 12.5 volts. I’ve replaced every piece of electrical in that car in the last year and a half: started, alternator, even the ignition switch. No ones found a problem in what’s left (the wires between them) but I hear that’s hard and expensive to check all of. Is this a sign of something bigger?
  2. I’ve had the PO420 code (from Check Engine Light) off and on for months. It used to be just for a day after a rain, but now it’s on most days regardless. Auto parts stores mostly reassure me it just means the catalytic converters or an O2 sensor might not run as clean, but that it’s just bad for the environment, not bad for my car (which matters, but money is tight so honestly it’s lower priority). Only one of the many articles I’ve read says it’s bad for the rest of the car. One or two sources say it can lower fuel economy, which I’ve checked and I still get 30mpg. I did the DIY test of spraying propane over the tubes in the engine as it idles to see if there’s a leak, but no luck. Word has it the O2 sensors are cheaper and easier to replace, but are usually not the problem; more often it’s the Catalytic Converter (for $300). Does anyone see a danger in leaving it there?
  3. Side note: my cars at 210,000. As a Toyota I hope I can get years more out of it.

The P0420, if it’s not causing any drivability issues, it can wait.

But the problem with waiting, with the check engine light on, is you won’t know if any new codes turn it on, it’s already on.

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Taking more cranking time before it starts than is usual, especially when it consistently happens after the fully warmed-up engine is parked for an hour, that suggests the possibility of a leaky fuel injector, problematic fuel pump, or its anti-drain-back valve. Before deciding on the cat ask you shop to double check all three of those parts are working correctly. For example if you have a leaky fuel injector that could eventually damage a newly installed cat. I presume you’ve already checked for other diagnostic codes. Has a fuel trim test been done yet?

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