C70: T5 auto, what feels like rough idle in park.

[tony209]

Got the above issue, feels like rough idle when in park but OK when drive selected. No fault codes showing in Vida but engine showing 0 and 10% difference from normal idle. Any ideas?

[JohnM 855 T5R]

Originally Posted by tony209

Got the above issue, feels like rough idle when in park but OK when drive selected. No fault codes showing in Vida but engine showing 0 and 10% difference from normal idle. Any ideas?

Most likely a fuelling issue at idle. When in drive, the ECU compensates by increasing the fuelling to compensate for the drag of the torque converter and transmission in order to maintain idle speed. In park, the fuelling is reduced (if it wasn't your idle speed would rise considerably). Could be down to a small manifold or intake leak, idle air control valve acting up or a number of other various possibilities. If you can read the fault codes that should give you some clue.
Failing that, it's just possible that the plug leads or spark plugs are on their way out. My old C70 (manual) ran fine when driving but developed a rough idle. Turned out to be a badly worn plug.

Regards
John

[SteveSarre]

Hi Tony

Which year is this?

Steve

[capt jack]

This exact fault on our S70 was cured by a new fuel filter, plus a clean-up of the dissy cap, rotor, throttle body an Idle Air Control valve.

Not sure if the T5 is set up quite the same as ours is a B5252S non-turbo with the Fenix management system, but from this and previous experience, random and mild tickover problems are very often simple electrical tiredness, or general maintenance issues.

ack

[Bonefishblues]

Does it feel rough in other locations too?

What?

What?

[tony209]

Thanks all, car is 2005, rough idle is only when in neutral or park, idle is smooth in drive with foot on the brakes. Not getting any fault codes, I did have a fault come up for the evap control valve or canister, I swapped the valve for a used one and it seemed fine for a few days then the rough idle came back but with no evap related codes. Plugs are about 18 months old and about 4k but worth checking. Fuel filter last changed about 4 years and about 18k

[SteveSarre]

Hi Tony

I dont have a 2005 in front of me. Wild guess, but cheap and quite quick to check.

Is there a vacuum hose that goes from a vacuum tree over towards the evap canister under the left front wing/subframe?

Is that hose intact? Is there a non-return valve in that line and is it functional (can you blow through only in one direction)? If there is a vacuum leak, if you block it does the engine run more smoothly?

Fingers crossed.
Steve