rough idle and acceleration in colder weather Topic is solved

Goldchemist · Post by **Goldchemist** » 03 Jun 2024, 20:15

I have a 2006 S60 AWD 2.5T. ~201,000 miles. I was having issues with a rough idle and rough/labored acceleration, only during colder months. No OBD codes. I did some troubleshooting, poking around. I noticed that on warmer days (>60 F) its wasn't as bad. I'm in the north east US so its mostly <60F during winter, especially at night. Checked hoses, air lines, tightened connections etc. Cleaned out the throttle body with a toothbrush, it wasn't that bad to begin with. Changed MAF sensor, checked air filter, air intake, turbo intake, changed the boost pressure /IAT sensor which as I understand also measures the temperature of the air coming into the intercooler. New fuel pressure sensor. Also changed the entire PCV system at about 170,000. Glove test showed slight vacuum. Change spark plugs and ignition coils at about 175,000. Now, as the temp is regularly above 80, its running very smooth, great acceleration, no issues at all. I read a little bit about the break booster check valve. Anyone think it could be that brake booster check valve? When its cold outside, I noticed the small brake booster pump running more than I think it should. Also read it could be the brake gasket/seal. But if that seal was bad I'd think I'd have some break issues and not only when cold outside. Any help is greatly appreciated. Thanks.

Post by **matthew1** » 03 Jun 2024, 21:07

Have you checked battery/battery cables/ground? Fuel filter replaced? What's your MPG? Does it go down in winter?

Post by **jonesg** » 04 Jun 2024, 11:12

check the reading from the ect sensor when the engine is cold.
get the reading, don't just swap it out with a cheap part.

Goldchemist · Post by **Goldchemist** » 05 Jun 2024, 16:04

thank you for the replies (I lived in Denver 2001-2005, loved it out there!)............New battery in ~March 2024. I did not replace the fuel filter. MPG goes down in winter. I checked the ECT sensor reading a few months ago and it was good. Temp was right on. The rough idle and acceleration occur only when the outside temperature is cold. even after the car warms up in the winter, lets say while driving to work, the issue still occurs. In cold months, I start it up, idles rough, labor on acceleration. I drive 15 miles to work, still rough, laboring acceleration. Now, in summer, runs beautifully. No rough idle, great acceleration. If the fuel filter was clogged wouldn't it still be running rough in summer? I understand how materials change in different temps but seems like something that senses the outside temp is not working. I read that the brake booster pump works in cold weather to prime the break booster. I'm thinking my break booster check valve is faulty. I will try to test that anway.

Post by **jonesg** » 05 Jun 2024, 16:49

I would smoke test it for vac leaks,
and read the fuel trims.

Goldchemist · Post by **Goldchemist** » 14 Jul 2024, 16:33

turns out my fuel filter was toast. I bought a new one but then compromised the fuel filter connector o-rings pulling them off. (I replied on another older thread so forgive me if I'm repeating here.). I should say, they were basically rusted on there. Nothing was getting them off without prying. The green o-ring is still stuck on the old filter and won't budge. That's how stuck they were. Hindsight, I should have changed the fuel filter many times over the past 202,000 miles. Stupid me. Anyone ever just put the o-rings back on the new filter and push the connectors on? It be great if I didn't need to replace the lines.

Goldchemist · Post by **Goldchemist** » 30 Nov 2025, 17:57

update on this one, turns out my electronic throttle body was toast too. Looks like multiple issues. The new fuel filter and fuel line likely were not the main cause of my rough idle. I replaced the ETB with one from FCP euro, not the official Volvo replacement but I think the Bosch model. Works great. Running much better these days.

Post by **jonesg** » 01 Dec 2025, 04:34

thanks for the update, I think VIDA would have found the throttle bady problem with a sweep test.

Post by **abscate** » 05 Dec 2025, 04:28

Goldchemist wrote: ↑30 Nov 2025, 17:57 update on this one, turns out my electronic throttle body was toast too. Looks like multiple issues. The new fuel filter and fuel line likely were not the main cause of my rough idle. I replaced the ETB with one from FCP euro, not the official Volvo replacement but I think the Bosch model. Works great. Running much better these days.

Hello fellow Islander. I’m on port Jefferson area if you need scanning help or just want to Volvolize.

We do cars and coffee first Sunday of the month in Setauket in the good weather