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C30 T5 first try cold start stumble

Old 07-11-2018, 02:22 PM
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Join Date: Jul 2018
Posts: 87
Default C30 T5 first try cold start stumble

I see this problem recurring in various threads but never see an answer, so maybe someone can help put this one to bed. My 2008 C30 acts weird when first started after sitting at least several hours.

1. The first try, it starts right up but stumbles until it dies. Adding throttle either doesn't do anything, or runs it to full throttle and leaves it there for a few seconds, even though I've let off completely.
2. The second try, the car runs perfectly, although the idle always seems a bit erratic, like it goes up and down hunting for a happy place, but runs smoothly. After five seconds, the car settles down and runs perfectly.
3. Turning the key on and off several times has no effect.
4. Cleaning the throttle body has no effect.
5. Disconnecting/reconnecting the battery solves the problem for a few days.
6. At all other times, the car runs perfectly with no issues at all. It starts perfectly unless it has been sitting and fully cooled off.
7. There are no warning lights on.
8. It does feel like the throttle is overly sensitive. The car is a bit harder to drive smoothly than usual. It seems like I'm a lead-foot.

It almost seems like the computer is having trouble booting up. Once it's up, everything is fine. Seems the most likely culprit would be an ETM problem. But I'm hoping someone has had the problem and will contribute their solution. Thanks in advance for the help!
Old 07-16-2018, 08:26 AM
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Join Date: Jul 2018
Posts: 87
Default Resolution

This was caused by a weak battery. It was still strong enough to start the engine with no sign of weakness, but starting drained the battery, then just as the engine starts, the headlights come on, the fuel pump starts, and lots of energy goes to energizing the alternator. This didn't leave enough to boot up the computer and the power drop simply was too great to run the electronics properly. After a few seconds of stumbling (or most times a restart) the alternator was able to energize and supply adequate power to the computer. And then the car ran fine until the battery was once again discharged from sitting.

If your battery is five years old, even if it seems to be fine, you should replace it anyway. The electrical demands on batteries is much higher now than on older cars.
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