Unstable revs when coming to standstill

Post by **TonyHayers** » Tue Mar 12, 2013 3:51 pm

I've had this for a while now, getting more noticeable. Seems to occur when coming to a standstill at traffic lights for example. Engage clutch as coming to a halt, the revs appear to drop below idle (say to 400-500rpm) momentarily and then jump straight to 1100-1200 before settling at idle itself (around 900rpm). This all happens within a couple of seconds and then idle speed appears pretty steady.

Anyone had this? I'm wondering if it's one of the clutch switches. I replaced the top one a while back which sorted a lot of jerkiness and fixed cruise control/start button, but I'm wondering if it's the other one?

Cheers.

Post by **Dave_M** » Tue Mar 12, 2013 4:22 pm

Tony

I get this occasionally. It's never stalled on me and I only ever get as you describe - ie it's not oscillating trying to find idle, but is almost like it gets caught unawares that you're coming to a stop and is a bit slow in "catching" the idle speed.

Is yours standard or modified? Mine's running an mrc Stage 2 map and Stage 2 inlet manifold - don't know if that makes any difference. I don't remember it doing it before the remap etc, but might be I just never noticed it!

Dave

Post by **TonyHayers** » Tue Mar 12, 2013 4:27 pm

Cheers Dave - no mine's stock map. I've got revolution intake, but it's been happening for a long time before that.

Post by **MikeFish** » Tue Mar 12, 2013 6:47 pm

Since I had the MRC stage 2, like Dave M I get a little blip of the throttle as I'm coming to a rest. I noticed it on the way home from MRC and it never did it before and has done it consistently since so I imagined it was part of the map. Sounds great with the exhaust! I haven't noticed any drop in revs though, just a blip of revs.

Post by **Audi Pardner** » Tue Mar 12, 2013 7:04 pm

My car's totally standard and sometimes when stationary the revs rise to about 1200/1300, then drop to the 'normal' tickover of 900 rpm after a few seconds. Doesn't always happen though

Post by **spikeyboy101** » Tue Mar 12, 2013 11:35 pm

Does the car start if you press and let go of the starter button, or do you need to hold the Sartre button down ?

Seem to recall fluctuating revs were a sign of the clutch peddle switch not working, as is the starter button.

So if you need to holder starter button down you need a new clutch peddle switch

Post by **TonyHayers** » Tue Mar 12, 2013 11:42 pm

spikeyboy101 wrote:Does the car start if you press and let go of the starter button, or do you need to hold the Sartre button down ?

Seem to recall fluctuating revs were a sign of the clutch peddle switch not working, as is the starter button.

So if you need to holder starter button down you need a new clutch peddle switch

Nah, already fixed that by replacing the top clutch switch (there are two). Just wondering if the other one could be to blame. Might just try it anyway for sake of £15 or whatever it is.

Post by **HEo2TEC** » Wed Mar 13, 2013 1:04 am

TonyHayers wrote:I've had this for a while now, getting more noticeable. Seems to occur when coming to a standstill at traffic lights for example. Engage clutch as coming to a halt, the revs appear to drop below idle (say to 400-500rpm) momentarily and then jump straight to 1100-1200 before settling at idle itself (around 900rpm). This all happens within a couple of seconds and then idle speed appears pretty steady.

Anyone had this? I'm wondering if it's one of the clutch switches. I replaced the top one a while back which sorted a lot of jerkiness and fixed cruise control/start button, but I'm wondering if it's the other one?

Cheers.

Mine does the same.

Post by **Dave_M** » Wed Mar 13, 2013 8:25 am

Same as Tony, don't need to hold starter button to start it.

Dave

Post by **WillRS** » Wed Mar 13, 2013 9:17 am

mine too - haven't changed clutch switch though yet - up at MRC on friday and will get them to have a look then.

my clutch was replaced not that long ago so i'm hoping its not that !!

Post by **usedcar** » Thu Mar 14, 2013 7:17 pm

Probably your air mass sensor is dirty and not reading the air properly so the car takes a moment to correct idle. You can get some air mass cleaner and wash it down. I use crc air mass cleaner. The adaptive values are probably a little off cause of this too and will correct itself.

Post by **TonyHayers** » Thu Mar 14, 2013 8:17 pm

usedcar wrote:Probably your air mass sensor is dirty and not reading the air properly so the car takes a moment to correct idle. You can get some air mass cleaner and wash it down. I use crc air mass cleaner. The adaptive values are probably a little off cause of this too and will correct itself.

Hrm. I didn't have any VCDS faults logged re. the MAF, but I can see that it might not generate a fault if it's just dirty. I didn't see any obvious dirt when I had it out recently but I imagine we're talking about microscopic amounts. Where can you get the CRC stuff in the UK?

Post by **usedcar** » Thu Mar 14, 2013 9:10 pm

you will not get any faults for this. The only thing that may show is a check engine light for a rich condition if real dirty. Otherwise if still within values for fuel trim but maybe close to max fuel trim will cause this behavior. also once the fuel trim gets back to where it should be your fuel mileage should get a bit better. So why this happens is your 02 sensor and mass are having conflicting info so when not moving your dme goes a bit crazy to correct.

Post by **TonyHayers** » Sat Mar 16, 2013 11:52 pm

Bought a can of the CRC mass air sensor cleaner and gave the MAF a good spraying then reset fuel trims with VCDS, will see if it helps at all.

Post by **TonyHayers** » Tue Mar 26, 2013 12:04 pm

Bit of an update here. It's been 10 days since I cleaned the MAF and reset trims and I'm pleased to report that I've not had the symptoms since

Not sure how much is due to cleaning the MAF and how much is down to resetting the trims in VCDS.

RS246.com Forum :: The World's #1 Audi R, S and RS Enthusiast Community