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Discussion Starter #1 (Edited)
I've been getting a rough idle and slightly hard start every now and then. She's a 2006 OR automatic, 240k km = 150k miles.

Symptoms:
  • It takes a few more turns that usual to catch, and once it's going the rpm fluctuates and the vehicle vibrates more than normal.
  • Giving it some gas steadies the idle.
  • Vibrations and RPM fluctuations stop after it's been running for 30s or so.
  • Has happened in cold weather and recently in room temp weather. Always seems to happen when engine is warm.
  • It's happened 6 or 7 times over the last 6 months. Once it happens it's more likely to happen again soon after.
  • No relevant codes. I've been ignoring a P0420 (cat converter/O2 sensor) that comes back every couple thousand km and some ABS codes, don't think they're related though.
A few possible rough idle causes I've found online are dying cam/crankshaft sensors, VVT sensors, fuel sender, coolant in cylinder via head gasket leak, and vacuum leak. I've ruled out the head gasket because it can happen without warning after the engine's only been off for a couple minutes, and the vacuum leak seems like it would be more consistent than this. It seems more like an intermittently failing sensor or electrical part. Spark plugs were replaced 10k km ago, MAF sensor and throttle body cleaned around the same time.

Anyone have any ideas on what might be causing it? Any ideas on how to check any of the sensors if they're not throwing codes?

TIA
 

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You can probably rule out the VVT system. VVT errors would throw a code pretty quickly and in my experience would occur after acceleration.

Have you looked at the pending codes?

Have you replaced the cam/crank sensors? Are they still OEM?

Good luck!
 

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Discussion Starter #3 (Edited)
You can probably rule out the VVT system. VVT errors would throw a code pretty quickly and in my experience would occur after acceleration.

Have you looked at the pending codes?

Have you replaced the cam/crank sensors? Are they still OEM?

Good luck!
No pending codes. I've replaced passenger's side cam sensor (the difficult one) with Hitachi and I've been carrying the driver's side in the glove box in case it dies. I'm usually in the "if it ain't broke don't fix it" camp. Haven't touched the crankshaft sensor and I think I'm going to go OEM when I do. It seems like all the aftermarket ones suck.

Do the shaft sensors often fail without codes?

Thanks for the info.
 
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