Interesting Cold Start Idle Behavior

a3inverter · Post by **a3inverter** » 27 Jan 2023, 17:06

Happy Friday all.

Wanted to share an interesting cold start idle behavior I've been experiencing this winter in hopes that someone might know the cause.

First let me describe what I've come to expect as NORMAL at start up (all ambient temps) after owning this 2006 V70 2.4 for 4 years:

Starts up, revs up to about 2000 RPM (I believe this is to create vacuum for the brake booster) then about 10 seconds of that, slowly drops down to normal (800ish RPM) idle speed.

Recently, in temps below say 33F, the behavior is different.

Starts up, revs up to about 2000 RPM, but then quickly drops to about 500 RPM and starts to lug for about 5 seconds then *bang* it pops back up to 2000 RPM, then does the slow drop to 800 RPM. This is a shudder that you can feel sitting in the drivers seat, like a valve opening or something. It's as if it wants to do the normal start up procedure, but something holds it back, then finally lets go.

This behavior only happens in cold temps (below 33F or so) at cold startup. It was 36F when I left work this afternoon and no evidence of this behavior at startup, nor does it happen during driving, or stopped idling at traffic lights, stop signs.

Any thoughts?

Post by **abscate** » 28 Jan 2023, 03:45

The p2 platform uses the VVT to make a high idle for emissions control. I always get it wrong but I think it opens the intake early to let extra air in to complete combustion in the cat, making it heat quickly.

If the VVT is messed up that will screw that up, but look for vacuum leaks first

a3inverter · Post by **a3inverter** » 28 Jan 2023, 06:08

Thanks abscate.

Additional info...

This behavior doesn't throw a code, however I have been living with a P0442 (EVAP Control System Leak Detected Small Leak) for a few months now. Was going to wait for warmer temps to figure that one out but maybe it's the culprit?

But...why only at ambient temps at or below freezing?

I just ran out this morning to test. Dash ambient temp showed 34F. Normal startup, no idle weirdness.

We are expected to have high temps in the 20's F near the end of next week. Ideal test conditions!

Post by **jonesg** » 28 Jan 2023, 20:11

wrong engine oil can and will make the VVT solenoid sluggish to react.

Also low oil level, the solenoid runs off oil pressure .

a3inverter · Post by **a3inverter** » 01 Feb 2023, 07:18

After several days of testing at various temps (including those below 32F) and an admission that the last time I had this issue upon checking the oil I found it at the low line of the acceptable range on the dipstick, I am ready to accept @Jonesg's theory on low oil level. I've been using Mobil 1 0-40w European Formula for the last 43k miles and made sure after that low oil observation to top things up. No problems since (fingers crossed).

Post by **scot850** » 01 Feb 2023, 19:10

I thought the recommended oil for a P2 V/XC70 was 5W-30 or 5W-40? What happens if you use the correct oil? Up here with cold winters the dealer uses 5W-30 synthetic.

Neil.

Post by **Krons** » 01 Feb 2023, 20:26

scot850 wrote: ↑01 Feb 2023, 19:10 I thought the recommended oil for a P2 V/XC70 was 5W-30 or 5W-40? What happens if you use the correct oil? Up here with cold winters the dealer uses 5W-30 synthetic.

Neil.

It is temperature dependent. From my 08 S60 2.5T manual:

: 33F2ADA0-7E5D-4BCB-AB8C-1A67B56620CF.jpeg (42.69 KiB) Viewed 1272 times

Post by **cn90** » 01 Feb 2023, 20:34

Probably bad ECT sensor.

If you have not replaced the thermostat, maybe it is time to replace it.
I use Wahler and there is a trick to replace w/o removing the PS pump.
Info in forum.

Post by **scot850** » 01 Feb 2023, 22:51

Interesting as the 08 S60 handbook is different to the 06 where the 0W-40 is not included as an option.

Neil.