My 2005 Flying Spur (European model) idles quite often with a slight periodic change (drop) of about 30 RPM. After the engine starts, RPMs jump (as they should), then drop below 500 RPM, then even out to 550 RPM in a couple of seconds and the car idles with some hesitation.

This becomes more severe when the day is hot (+30°C/86°F), probably because the A/C is working harder so there is more load on the engine from the A/C compressor. Idle speed also reacts quite greatly to the turn of the steering wheel. Sometimes the engine dies right after Drive is selected.

The car gives no error codes, no faulty sensors etc. Vacuum pump works only for about 20 seconds after start, so the vacuum lines should be OK I think.

Slightly richer mixture can be observed when the idle is inconsistent. There is also a 100-200 RPM oscillation at around 1,300 RPM at slight throttle which is perhaps a sign of an issue in the torque converter.

Otherwise the car runs very well, with no power loss when accelerating etc.

Any ideas where to look for the possible cause?

Thanks,
Tadas

 

Just disconnect you battery for like maybe 5min. Reconnect and let your car relearn.
I had similar issues with mine when I got it.

Cheers,
~ZaOs~

 

Many thanks for your reply Zaos.

I finally had a chance to check your suggestion, however it made no difference. Any other ideas?

Thanks,
Tadas

 

​​​​​Lazy MAF sensors can cause this problem. Sometimes they don't throw codes if the parameters are close to the factory mapping standard. Scan the fuel trims. At least try cleaning the MAF sensors.

 

yup , my right bank MAF was bad, but only at certain temperatures, replacement sorted all my idle issues, hope its as simple for you

BB

 

If the Mass air sensors check out, might also check your throttle valves to make sure the operate freely/don't have a bit of dust buildup. I've had similar issues when the throttle body wasn't fully closing at idle due to thin a layer of gunk.

 

mine was idle air temp sensor. It had oil residue on it. car will start always when cold when hot will cut off sometimes or not start unless one foot is on brake and other is giving it gas