'99 S70, FWD, Auto, Non-Turbo -- Stumbling Idle on Start-up, No Codes

Post by **E Showell** » 03 Jan 2016, 09:49

Pretty much what the title of the post states. I'm getting a stumbling idle -- say between 1K and 1200 RPM right on start up before the engine is warm. The care has a rebuilt XeModex ETM, newish (less than 5K) plugs and coil packs. Thermostat and ECT are newish as well. I don't think it has a vacuum leak, but I can't definitively rule that possibility out. When I give it a little gas it stumbles even more with the idle dropping even lower. After I drive for a bit and things have warmed up, the idle seems fine.

Any thoughts?

Edited to add that this is an infrequent occurrence. By no means does it happen on every start-up. Maybe every 25th start and seems to happen more often if it has gotten really cold the night before, but that could just be a coincidence.

Post by **E Showell** » 15 Jan 2016, 11:36

I don't always buy gas at the same place. Now I'm thinking it could be a bit of water in the gas. Got about 5 gals. of fuel last night. Tank was still at less than half after the fill. Started this morning with the stumbling which went away once the engine warmed. Is this just water in the gas getting burned off?

obayha · Post by **obayha** » 15 Jan 2016, 12:06

If it breaks, we can usually say what the problem is. In this situation, you may be heading in the right direction. Maybe some high octane for a tank or two and any additive that will remove water and go from there. A coil could be breaking down, as it did with me, but mine went quicker than yours is doing.
When you say "stumbling" meaning not running on all five? and then it catches up. Jump out and pull the fuel rail, one by one, like I did and find if it is local to one plug.
Shane

Post by **E Showell** » 15 Jan 2016, 12:11

Thanks Shane. All coil packs replaced w/Bosch units about 7K miles ago. All spark plugs replaced with Volvo plugs at the same time. Battery is new, and upgraded to a Group 48, as well. I feel like it could be missing, but I'm not certain.

obayha · Post by **obayha** » 15 Jan 2016, 12:30

With gas prices down, it may be worth the octane boost and see what happens.
In South Carolina yesterday it was $1.54 for regular.
Shane

Post by **E Showell** » 15 Jan 2016, 12:55

I always use at least 89 after burning an exhaust valve a few years ago.

Post by **abscate** » 15 Jan 2016, 13:21

I think water in the gas is a lot less common than people think - and it won't get better when the engine is warm.

If you put a whole can of HEET in with 5 gallons in tank, that should put any water to bed, unless someone has really negative ju-ju for you.

You could break the fuel line at the junction with the fuel line release tool , fill a 500 mL glass container and look for cloudiness to confirm water diagnosis.

Post by **E Showell** » 15 Jan 2016, 13:23

I might think vacuum leak, but it is so intermittent and I'm not getting any codes setting.