Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

2002 VW Jetta Ignition Coil(s)

My 2.0L Jetta had an intermittent misfire, only at idle. I took it in to the shop, and they fixed a vacuum leak and replaced the plugs. The car drove home fine, but the next morning it was misfiring at all speeds. When it got back to the shop, they said that the coil pack was bad, and it would cost another $240 to fix. I couldn’t help but wonder if they might have done something to cause the pack to fail, since it seemed to be working fine before I took it in. Their explanation was that the coil had become accustomed to sparking at an adjusted (more powerful) setting to account for the vacuum leak, and when it tried to go back to the factory setting, it quit working. Also, all of the stress from running at a higher output wore it out. Most of that sounded pretty booooogggguuuss to me. Do you agree?

Well the logic is bogus, but that doesn’t mean they did anything wrong. If they had to replace the plugs, then you could have had a misfire due to a bad plug. Every time a plug misfires, it can do damage to the coil. The coil has to spark somewhere and if its not through the plug, then it arcs internally. These internal arcs eventually take their toll on the coil and it will fail.

Aged spark plugs or plugs in which the gap is wide can shorten the life of an ignition coil by making it work harder.
One often wonders how often plug gaps are checked and adjusted as necessary even though conventional wisdom says that plugs are pre-gapped. (Not my opinion though)

I sort of half agree with what they’re telling you, assuming there’s not a misinterpretation between what you were told and what you’re relating here. It could be amtter of not articulating it properly and we’re all guilty of that at times.

Certain year VWs (e.g., my 2004 Passat) were known for bad coils. You might want to check and see if your should have been replaced under a recall.

Thanks, I am glad to hear that it is plausible for a coil to fail in those circumstances.