Hi...
I observe a very slight roughness when car is in idle (at traffic light e.g.). It appears like once a minute or so and is like a slight cough.
I think it is not a big issue but I would like to find the reason before it gets worse.

Car is a MK IV Golf, year 2002, I think AEG engine with about 76k miles. The o2 sensors, cat have been replaced at 60k. The spark plugs, cables and coils have been changed at ~55k. The throttle body is as clean as a dinner plate. I changed the air and fuel filter recently.

I do not read any trouble codes via OBDII (again, the roughness is by far not as bad as in case of a misfire).
I captures RPM and air mass using VAG and attached diagrams. The car was in the parking lot, got a ~5min warm up and I just pushed the throttle a bit once in a while.

Does anyone have an analytical approach to track this down, I have VAG available and could run some other tests.
Maybe you find something suspicious in the data I have attached, though an IDLE rpm of 760 sounds good to me.

Thanks,
Marcel

PS: I don't want to arbitrarily replace parts to get rid of this, so please, no 'I could be this and that' answers. Would be great if I could exclude something by having a closer look or running a few test...

Message was edited by: Racoon

thanks for the input...
I did a quite intensive test drive yesterday and checked the misfire ctr. Rock solid 0 for all cylinders. I did a fair amount of driving in different conditions as well as long and short idle periods.
so no misfire as it seems..

any other ideas to look for...

Marcel

PS: it seems as its getting worse at some points, were it is like a gentle pull on/kicking of the engine...

thanks man, I will look into block32 tonight and post results.
Isn't 032 the oxygen sensor??

Why were the cats replaced?

kind of sounds like a bad maf sensor but could be as simple as bad motor mounts.

Hi Rick...

I think you suggested to monitor the MAF voltage some time ago (miraculously this reply disappeared??)
So I did a testrun. Find attached results, first page showing air mass, rpm and inj.period as a function of acquisition time and on the 2nd page I plotted air mass vs. rpm.
I don't know if that makes sense but I just did it, it almost looks like that for some operational condition one should get a linear behavior (for others e.g. throttle off maybe not, which would reflect all the points below the line)

Let's see if someone can make some sense out of that. For me it doesn't look like my MAF is bad, but any comments are welcome.

cheers.. Marcel

I'm also looking for the same solution. Daughter's '02 1.8T has an occasional temporary shake, like it looses spark or fuel control for a fraction of a second. She notices it more often with A/C compressor on, also has stumbled at idle enough to shut off. I've serviced all of the likely electrical connectors in the engine area. No MIL, no codes, clean throttle and MAF. I have a new ignition switch in case the problem is as simple as that, haven't installed yet, but that would set a B+ code, wouldn't it? So I am also open to new suggestions!