high idle speed

[sun and kath]

My idle speed is slightly high, (s4, 1999) starts okay when cold, but then after a very short itme has a high idel that fluctuates betweem 1000rpm and 1400, and the engine takes longer to drop down to slower speed when lifting off throttle.

VAG COM gave no fault codes
I have had a quick look for intake leaks buy not sure how to test for these.
Can anyone suggest how i should investigate?
cheers

 

[sun and kath]

OK. still have a high idle and the car seems a bit "lumpy" when off throttle. I rigged up a funnel and pipe to the air intake just after the MAF, blew in, could not find a air leak. Air did get into the crack case by the valve connected to the aluminin housing after the MAf. When I blocked this off all seemed air tight.
WOuld this suggest the MAF has failed??? any suggestions, reading the measuring block on VAG COM when "idling" at 1200rpm the mass air flow is circa 10.2 g/s. is that right or a duff reading. Like wise, when the outside temp was about 5 degrees C, the intake air temp was 30 degrees c, is this a duff reading or right coz of engine temp heating it up. If a dusff reading is that the MAF or some other sensor?

cheers

 

[shineydave]

i thought at idle the MAF reading should be around 4-6 or thereabouts, it tells you in Vag-Com what the acceptable range is.

have you logged it whilst running a FATS time, that might shed more light on whether it's the MAF or not

 

[sun and kath]

Well if 4-6 g/s is normal , them 10 g/s may be a correct reading considering mine is idling at 1200rpm.

What is the FATS time? how do i do that?

thanks

 

[shineydave]

FATS is a standard test to check how well an S is performing, it measures the time to accellerate from 4200 to 6500. you start logging block 003 and then boot it from about 2500 untill 6500. the log can then be put into an online FATS calculator ( http://ctny.audiworld.com/mark/s4/ecux/fats/4200-6500_fats_time.xls )that will extrapolate a time. standard car will do it between 6 and 7 secs, stage 1 should be just over 5. no cheating, level road, no downhill runs, lol

 

[sun and kath]

Look forward to that, hope the snow forecast up here stays off Monday then!

Any particular gear for the test?

 

[shineydave]

sorry, forgot to mention that, it should be done in third

 

[sun and kath]

Fixed !
My high and variable idle is now fixed. I did go through changing the MAF, my car must have already had this changed as the old Maf was dated 2002 on my 1999 car, now it has its 3rd MAF. This did not fix the fault. I then found by trawling the net that a disconected battery can cause the throotle body (Drive by wire) to go out of sink and require re calibrating. Of course last month my battery went and i fitted a new one! So after 6 months on the shareware VAG COM, i finally spent 99 dollars (hopefully under £60) and ungraded to the full version and re calibrated the throttle and it is now fixed. I am well pleased. Shame I blew £90 on the MAF!