Hi all,

I'm having a problem with my wife's 2002 A6 3.0 CVT, 91000 miles. When driving any more than idle, up to around 50-55 MPH, the engine constantly and rhythmically jumps or surges RPM (probably 100-300 RPM). At 55 MPH though, it stops and runs smoothly up to...oh say 100 or so (I wouldn't know anything higher than that). It seems to be more pronounced at lower speeds or when accelerating, and makes for some very jerky starts and not very smooth city cruising.

I have a VAGcom, but no service manual. About 8 months ago I had a CEL and I checked, stored and cleared it on my laptop, it mentioned a sensor from what I remember, but the laptop crashed since then and had a rebuild. The light came on again after a few weeks, until my wife bothered me enough to clear it so she could get it inspected, and in the process I forgot to save it. I'm now driving it instead of her so that I can try to get the CEL to come on again.

Has anyone else experienced this behavior? And if so what was the solution? I'm at the point of assuming that an O2 sensor is my problem and just replacing it/them, but I'd like to see the CEL proof first, and the experience of anybody else.

Thanks!

 

probably the idle control unit. That would cause sporatic idleing. Could also be the Mass air flow sensor, really need a code or the car to see for sure. You could disconnect the MAF and see if it runs better, if so, that is your culprit.

 

The car runs smooth at idle, either in gear or in neutral. I will try to disconnect the mass air at lunch to see what happens.

I dug around the old backups from my laptop and found the old logs from VAG. The pertinent one seems to be: 16805 - Warm Up Catalyst; Bank 1: Efficiency Below Threshold P0421, if that helps.

Thanks again.

 

Sounds like a MAF problem, I had the same problem with our Infinity.

 

I disconnected the MAF to see if it would help. The idle immediately was worse, but it did not help with the surge problem. I finally got it to throw a code again, so I'll check it this weekend and see if it is the same P0421 code.

 

P0421, Vag 16805 Warm-up Cataklyst efficiency below threashold bank 1. Your catalitic converter could be shot. You need to check the O2 sensor heater before the Cat and the O2 sensor behing it.
Does your engine feel restricted?
Loss of Power lately? it may have come on gradualy.

HAVE YOU HAD ANY MISFIRES??? P0300,01,02,03,04,05or06.

If that is the case you will also need to find what caused it to fail.

 

Went out of town last weekend, didn't get to check the code yet. But, there have been no misfires either reported or felt up to this point. Power loss would be hard to gauge since I've owned the car less than a year and my wife has been the primary driver, but from what I remember when I first bought it, it feels the same, no restrictions, no loss of power. Like I said earlier, once I get above 55 mph, it is smooth as silk. If I accelerate hard from a stop, it also doesn't seem to surge very much at all.

I think I said before that the idle is also very smooth, and when not in gear it revs smooth, and holds revs in the "trouble zone" without any fluctuation. I'm actually very concerned that there may be a transmission problem instead of engine problem.

 

i have a 2002 audi a6 quattro,. mine is doing the exact same thing. sugeing when under 50 mph then stoping once i get above that. i just got my fuel pump replaced thinking that would solve the problem but it continuing. however now the car will surege more wen the AC is on. any suggestions of what it might be?

 

Surge can be the cause of multiple things.
broken vacuum line
throttle control
maf, or other sensors

you have to have the codes pulled with a vag com.

If you haven't replaced the vac lines in last few years replace them all they get brittle and crack. and it's cheap easy maintenance.

 

My 2002 Audi A6 3.0 is doing the same thing...surging 100-300RPM between like 30 and 55MPH....above that all is smooth. At idle it runs smooth most of the time but every once in awhile srges bad. I checked all the vac lines and cleaned the MAF sensor with no luck. If it was a vac line or something mechanical wouldnt the problem be there all the time? Why intermittent?
Other options/ideas?