'08 S60 2.5T stutter on start

[mrbrian200]

13% I'm pretty sure that's sticking part way open if the engine is at operating temp/low idle. Around 13-14% is what I remember mine sticking at. The spacing of the gear teeth when they wear will stick at roughly multiples of 6-7%. Idle was lean and 'harsh' all the time which felt like all the engine/subframe mounts were bad, but they were fine. On the occasion where it sputters really bad on a cold start does it rev up or does the idle speed stay down below 1000 rpm and feel 'choppy'? These would be the times when it doesn't open up, which on mine would start to happen below around 35F cold start in the morning, the colder it was the more likely it would do it, but not every time.

As the wear progresses you might start seeing DTCs for MAF and Fuel Trims while idling or cruising. Unplugging the MAF seems to make things better for reasons not fully understood because I don't know what data the ECM reverts to when it's disconnected. Note: don't plug or unplug the MAF while the car is running. This can spike the internal circuit inside the MAF and damage it.

[MOZKNBBUHD]

When it sputters it revs up to a "fast idle" of around 2000 RPM (little more when it's really cold, little less when it's a bit warmer). It seems to happen more often on a "lukewarm" start, where the car doesn't quite make it to operating temp, then gets left for a short time (<1hr) and then restarted. That seems to make the problem happen most often. Letting the car sit for a while seems to prevent the issue, as it never happens in the garage in the morning (heated to 45 deg F), and rarely if ever happens after work.

[Zeeko]

Hey fellow Minnesotan-

I just had a very similar problem with my '04 2.5T- it was fine after I bought it, but progressively got worse with regards to starting and seemingly worse with the onset of winter. What ended up solving my issue was changing the fuel to strictly 91 octane. 89 was not cutting it- I'm not sure if it's because the 89 in winter Minnesota has a bunch of anti-freeze additives or what, but it was causing problems.

[zanzabar]

viewtopic.php?f=9&t=73914

Sounds awfully similar to what I went through on my '07. Ended up being a marginally weak battery after throwing a bunch of parts at it (injectors, ETM, MAF, crank position sensor, different octane). If your other ideas don't pan out try throwing a new H8 battery in it.

[RickHaleParker]

Your fuel pressure maybe marginal and get worse when cold. When cold, turn the key on wait for 5 seconds, then try starting. See if that makes a difference.