My daughter said he Jetta started but idled rough at low rpm (less than 600). The CEL light came on. The next day it started and ran fine but she took it to a shop for a checkup and oil change. Shop could not find anything suggesting rough idle/hard start but did find the car down a quart below min line. 98,000 miles, last changed at 87K14 months ago. Shop said it must have run rough because of the low oil level. I’m not sure I see the connection. Any ideas why oil is down? No leaks on the ground. Head gasket?
The engine is probably burning the oil.
Start keeping an eye on the oil level.
Tester
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Then there should be a diagnostic code stored in the computer’s memory. Ask you shop for the code number, usually would be something like “P0300”. Post the number here for more ideas. It’s possible the low oil level caused the poor idling, but my guess, that’s unrelated.
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98K mile engine with oil change intervals of 11k miles (km?) … If your daughter doesn’t check her own oil level regularly, you should teach her how and how to add some when it gets low or she will kill this engine.
There should be no direct relationship between 1 qt low and an idle problem.
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An engine that burns one quart of oil in 14000 does not have ab oil burning problem. Many brand new cars burn far more than that.
This car has an owner neglect problem. Thr oil should have been changed every 10,ooo or 1 year whichever comes first but thad is not as serious as not checking the oil in all that time. It is not up to anyone else but the owner to maintain the oil level. Even if it was a brand new car, no one would honor a warranty claim if you brought in a damaged engine with no oil n it.Omce a monthwould ne often enough to check it. Do not let it gry over onr quart low.
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If the last oil change was 11,000 miles ago, that doesn’t mean that it burned a quart evenly over 11,000 miles. It’s possible it burned it all in the last 5,000, or 2,000. or 8,000. There’s no way to know. Also, it may not have been full after the last oil change. If it did burn it evenly over 11,000 miles, that is not considered significant. Again, who knows? Checking the oil going forward will answer that, as others have suggested. The rough idle may be completely unrelated. The only connection I can see between burning oil and a rough start idle is leaking valve steam seals which would most likely have gray/blue smoke coming from the tailpipe on start-up.
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I think the OP said it was a quart below the minimum mark, which would make it 2 quarts low.
Missed that @jdmere. You are correct sir.
2 quarts low on an engine that holds 6.3quarts is effectively 1/3rd low.
I agree with others that now is a good time to teach your daughter how to and the importance of checking the vehicles engine oil on a regular basis.
On a personal note, 11,000 miles (and 14 months) is too long on an oil change. these need to be done per manufacturers instructions.
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Let’s also remember that VW has a specific oil requirement, and just dumping in a quart of whatever 5W30 you have around is the wrong oil for the car any may cause accelerated engine wear, especially if going with extended oil change intervals.
If I recall, that car needs VW Spec 502.00 engine oil. Are you using a European spec Synthetic oil?
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Thanks for all your replies. Yep, need to change that oil more often and keep an eye on it for now. We’re using the correct oil too.
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I read that the oil pressure controls the variable valve timing. If the oil is low, maybe after sitting for a few days, the oil pressure wasn’t available on startup for the valves and it ran rough until the pressure was there. Not a good sign for the valves if that’s the case. Thanks for all your input. Case closed
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This may also be the source of the CEL. It’s not just the level of oil but the quality of it. If I delay changing oil too much beyond the recommended interval in my truck, It starts running a bit rougher and sets a code for the cam phasing. Oil not low, just used up and viscosity no longer up to the task.
It’s good you’ve got this oil issue resolved and your VW is presumably idling and running well again . Valve damage due to a variable valve timing malfunction seems pretty unlikely. The VVT function is used advance the valve timing at higher engine rpms to allow more time for the gasoline to move into the cylinder. If that didn’t happen it might affect the idle or running quality, emissions, etc, but wouldn’t normally damage the valves.