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Discussion Starter · #1 ·
I'm noticing that my car is shuddering when I shut it off... the intensity of the vibration varies from time to time, but when it shudders hard, I notice that the car isn't running very smoothly. I'm sure it wasn't shuddering like this before. Anyone knows what gives?
 

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Is it pre-ignition? The car fires a few times after you shut off the ignition? What fuel are you using?
 

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Discussion Starter · #3 ·
I dunno exactly what pre-ignition is. But itt feels like a vibration throughout the car for less than a second.

I use 94 or 92 octane at Chevron and never have tried using anything less than that.
 

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An Old school term for detonation after you've shut down, sometimes caused by Low Octane fuel. If the car was running you'd say Pinging or Knocking.
 

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I haven't experienced pre-ignition run-on since I started driving fuel injected cars.

What is the mileage on the 2003? If the car is continuing to run after shutdown it may indicate a hot spot in the combustion chamber. This may be due to carbon deposits or spark plug problems. If it is plug-related, I think it is possible that someone installed the wrong type (e.g. heat range) plugs. The Trionic system also uses the plugs as knock sensors, so you have to use the right ones.

Other possibilities include a vacuum leak leaning out the A/F mixture.

On any 2003 there are two things to always check at this point:
1) Are you on the original battery? If so, it should be replaced. Not likely to cause the problems you are describing, but these batteries do not last 5 years without measurable deficiencies.
2) Inspect the SAI check valve for leaks. Small leaks can cause A/F problems in the short term, and severe wallet-draining problems in the longer term.
 

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Discussion Starter · #7 ·
Thanks guys... I'll check the SAI valve. But how can I check for a vacuum leak?

btw, the battery is only 8 months old. The car has 67000 kms on it.

Thanks again. Always so freakin helpful!
 

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jochi said:
Thanks guys... I'll check the SAI valve. But how can I check for a vacuum leak?
These can be hard to find. One location that is prone to leaks is where the purge plumbing enters the intake manifold. This is right next to the oil dipstick. There is a short run of tube that connects to the engine, then tees off left and right just behind the dipstick tube. The short tube seems prone to cracking. You may need to remove the plastic engine cowl to get a better view.
 
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