1995 456GT rough idle at startup - Ferrari Life
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post #1 of 6 Old 08-23-2012, 06:38 PM Thread Starter
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1995 456GT rough idle at startup

I have owned my 456 GT for over 10 years. Car is serviced by dealer but each year at startup the car seems to have more difficulity starting. I follow the instructions from the dealer when purchased which indicated do not move throttle until after the engine has smoothed out. I always warm up the engin before I drive. When started it will stumble for about 30 to 45 seconds then attempt to clear itself out and come to a smother idle. However every year it stumbles a bit more and has now developed a miss at 3100 RPM. Dealer has balanced the fuel rails, cleaned all injectors checked plugs and wires. I also drain the fuel before startup at beginning of spring and replace with fresh fuel each year before car is driven. Any other owners having this type of issue or do I need a new shop?
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post #2 of 6 Old 08-23-2012, 07:07 PM
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I have had some client cars with rough idle and found intake gasket leaking. I also have found bad airflow meter with some v12 cars. Check these issues and good luck.
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post #3 of 6 Old 08-23-2012, 08:06 PM
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Alex- Yup, the intake manifold bolts on the 456s and Maranellos seem to want to loosen if not torqued regularly.

Terry Phillips

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post #4 of 6 Old 08-24-2012, 02:41 AM
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@GJK: Have the injectors actually been taken out and sent off for a deep cleaning, or did the dealer simply run a quickie cleaner through them via the fuel rails or fuel tank?

Gummed up idle air controllers are also known to cause idle issues - they should be cleaned periodically too.

Have you tried a fresh set of Iridium plugs?

On the ignition wires, I would "carefully" hang an inductive ignition timing light on each cylinder's wire and ensure you're getting a regular firing pulse. If you find a cylinder that looks to be firing erratically, that's probably your misfire. (Emphasis on being careful here as 1) if these are the original ignition wires, they're probably getting somewhat brittle, and 2) if there's an ignition leak on a wire that you're handling, you could get a nasty shock)

Lastly, our cars (456/550) have been having issues with the rubber fuel pump cushions disintegrating over time and bits of the rubber plugging up the intake of the pumps. While this shouldn't appear as a misfire per se, all of us who are driving these older cars should have this checked, as any/all of the soft goods inside our fuel tanks are being destroyed by the ethanol in modern fuel. You or your dealer could hook up a fuel pressure gauge on each fuel rail and check for fluctuations in pressure, which could be a tipoff of this problem. Here's a link to a thread by the latest 550 owner who's experienced this problem: Another Case of Dissolving Rubber in the 550 Gas Tank

'99 550, Rosso Corsa / Nero, S/N:114654, Assy: 31836, Engine: 52084

High mileage, low compression, and missing on a few cylinders.....just like my cars.

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post #5 of 6 Old 08-27-2012, 07:05 PM Thread Starter
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Thank you for the input. I will now get started on the fix. What a great process for helping out with these questions.

Thank you again.
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post #6 of 6 Old 08-27-2012, 07:47 PM
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Welcome to FL, GJK.

The only thing that I can add is that do not assume that having things done at dealers is always done properly.

Good luck with the resolution.

w/ smiles


PS. If you PM one of our newer members, Akaiakuma, who seems to know 456 in and out, he may help you with the answer.
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