Smog test: Car not holding revs

B6/7 S4/RS4
#1

Guys,

My 2003 B6 is having problems getting through the UK fast idle smog test. The car is revved up to 2500 has to be held at this rpm for 30s. The problem is that the revs keep on climbing beyond 2500 and if you try and modulate the throttle all revs drop off.

The car has deleted pre-cats and 100 cell sports cats. It also throws the following codes on a regular basis:

17522 - Oxygen (Lambda) Sensor; B1 S2: Internal Resistance too High
P1114 - 008 - Implausible Signal

16524 - Oxygen (Lambda) Sensor B1 S2: No Activity
P0140 - 004 - No Signal/Communication

The sensors themselves were replaced due to the same set of codes but did not make any difference. In summary does anyone have any ideas how ot maintain revs or is the problem related to the codes.

Thanks in advance

#2

Well if your getting the 02 code that would explain the car not being able to hold revs for that long. The car isn’t getting a signal from those back 02s so it’s probably adding fuel. Try doing the Rev test at home then if it is still not able to hold pop the hood and unplug the maf try again and let us know if that fixed it. If not the next step is to reset the throttle body.

#3

Thanks for the response.

Tried it again this morning and was able to hold 2500rpm for a few seconds before the revs died. It was like a trip switch was triggered. Very odd. Also, more often than not, the revs rise noticeably during low gear changes at around 2000rpm. I will unplug the MAF at lunchtime and try it again. TBA was done a few weeks back.

#4

UPDATE II:

Reset the TB and again tried to hold the revs. No joy. Could not even modulate the throttle. Tried Feathering the throttle but the revs would either die or increase

Disconnected the TB and was able hold 2500rpm. It was easy to increase or decrease the revs.

It looks like a new TB is on the cards.

#5

I mean MAF

#6

I changed the words in my quote for you. I hope the advice helps. Good for you sometimes I give advice and the people just keep complaining about issues but not following the diagnosis possess.

Pulling the maf will help fund or make some issues more easily seen. In this case your maf might be bad or you pulling the maf is just covering up and helping sort out a bad mystery vac leak. You can get a replacement maf for investigate further by taking some starter fluid and spraying around the vac system and pcv system to see if it effects the motor rpm.

#7

Thanks for replying. I had no starter fluid so sprayed butane gas and there was no change in the revs. But I’ll will get a can of SF and try that before buying a new MAF.

#8

It’s always good to check. The unplugged maf can help the car run better incase of a vac leak.

#9

Gave all pipes, junctions and connectors a good spray of SF and there was no noticeable change in the revs so I’m going ot bite the bullet and get a new MAF. Hopefully, it will solve the rev issue as well as the codes that keep on being thrown. I am also going to check the earth bonding point to make sure it is clean and corrosion free.

#10

That is always good to hear. Take off the pcv system and give that a good cleaning and check it for possible leaks as well. It’s a good thing to do. The spray is like 2$ insurance that it’s probably the maf. I know a few guys that didn’t listen and they spent the , one on a maf that didn’t need replacing.

#11

Fitted the new MAF and the revs are holding nicely. The throttle is now easy to modulate. Need do some more trips before checking to see if the codes have gone away.

#12

I hope I was helpful. If so if you see others looking for help on other websites send them here.

Also reset the ecu and after you do leave the key forward for 45 seconds before you start the car. It will reset and relearn the throttle body and ecu. This way any stored values will be reset.

#13

Update:

Car is definitely driving better after replacing the MAF and resetting the ECU. However, it is not possible to consistently hold the revs and the rev surge is still evident during gear changes (2 to 3). Again, this is not consistent but an improvement. I going to throw another can of SF at the pipes in order to search out any leaks

#14

Sounds like a gremlin is still in there somewhere. Are you on a stock tune. What exhaust do you have. Also how old are all your maintenance things like coils plugs and oil filters. Any feed back on the o2 sensors how old are they.

#15

Car was tuned several years ago and the exhaust is custom made. Car is serviced annually with new oil and filters, although yearly is probably an overkill because I do less than 6k miles a year. Plugs were changed less than 3yrs ago along with the o2 sensors. The coils were replaced about 5yrs ago along and the cats are about 8yrs old. Can either the cats or sensors be toast after such a short time and low mileage.

The last scan only produced DTC 16524. So the fixes so far has resolved the 17522 DTC.