No power, rough idle and 6500rpm limit

B6/7 S4/RS4
#1

Evening All,

Car has started to run rough, cold start is extremely rough and the revs move up and down a little during the process, once cold start is finished it settles a little but still stumbles and is not smooth

Car lacks any power at all

Whilst trying to log a 3rd gear pull and capture some data the car limited itself at 6500rpm

Any ideas?

No fault codes or dash lights at all

Plugs are new and injectors have been out and cleaned recently, coil packs haven’t been changed but i would of thought i would of had a flashing EPC light if it was a coilpack?

#2

Is the car stock. What was the last work you have done on the car and how long ago. 6500 is limp mode especially on a RS4

#3

Car is a B7 RS4, last work was injectors out for cleaning but the problem was there before this and the injectors made no real difference

Car is not stock, gutted pre cats, miltek cat back exhaust, cold air feed, BMC panel filter, and the car was mapped many years ago

The strange thing is I have no fault codes

#4

Well, I’d say something is off. A 6500 max rpm means there is something wrong happening.

Remapped ECUs can be great but, you have some companies that just turn off every error in an attempt to help make more hp. Now I’m not saying that’s 100% what’s happening. But generally if the car is in limp mode you see codes. Might make sense to just flash back to stock to test.

Did your readiness all run?

#5

I was going to say. One of the issues with the RS4 that can cause havoc is the 02s. But if your tuned and loosing power and not getting codes make sure the 02 are actually working. As CV said depending on the tune you never know what has been turned off.

#6

Any ideas on best way to tell if 02’s are working as they should?

Looking at readiness they all look to be passed when checked but think some of these can be set to pass when tuned

#7

You can look at them in VCDS.

#8

What am I looking for? As far as I can see both sensor 1 voltages on each bank fluctuate up and down between 0.1 and about 0.8 volts so believe they are working ok?

#9

It’s actually hard to say. They’re sending information but that isn’t telling you if they are working ok.

unplug the MAF see if the car runs better. Then check fuel trims. make sure to check for codes on both ECUs .

#10

Ok will give the car a run with MAF unplugged, MAF was new end of last year

Checked for codes on both ecu’s and they show nothing

#11

Yeah no codes is not good. Might not be a bad idea just flashing back to true stock to make sure there isn’t something blocking any potential codes from popping up.