VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - philip308s

I have a VW fox 1.2, 2010, CHFB engine code, 95K on the clock. the car randomly looses power for a few seconds at low speeds, also once stopped at the light etc the idle will be very poor for around 10 - 15 seconds as if its gone into limp home mode, no warning lights are displayed, no fault codes found when I plug in the OBDII device, I have changed all coil packs, spark plugs, fuel filter was done recently, air filter, new injector seals, the 02 sensor has been replaced recently. also the timing chain was replaced at 80K. I've also carried out a compression test which didn't show any problem.

this has been going on a few months, cant find anything online about such a problem and I dare not go to VW as the last time the car had a misfire they couldn't find it.

if anyone has any ideas its much appreciated, I've tried to explain as best I can.

Many thanks

Phil

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - bathtub tom

Does it have a MAF sensor, if so a delicate clean may help.

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - elekie&a/c doctor

Looking at the evidence here, as it is a 3 cylinder vw engine, I would hazard a guess that you have a burnt valve(s). Not enough to show up on a compression test. No maf sensor on these.

Edited by elekie&a/c doctor on 09/06/2019 at 20:56

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - philip308s
Hi again, so today the engine management light finally came on and showed 3 codes:

P0420 - catalyst system efficiency below threshold bank 1
P0171 - system too lean bank 1
P0172 - system too rich bank 1

Hope it’s helps cos I’ve got no idea now!

Thanks again

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - elekie&a/c doctor

The cat code is not related to your problem. There are plenty of cars running around with this fault and the engine works fine. The other 2 codes could be related to an air leak in the induction system. A non sealing oil filler cap, engine crankcase breather issue, can bring on these last 2.

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - 3uga

You should check the egr. I find it weird that your car has code for rich and lean. All the codes are related to to the o2 sensor. If you have a elm you can read map, maf and intake temperature. If they are transmiting data, you shoud go for egr clean and check for any intake or exhaust leaks.

From what ive seen, when egr error apears on vag you usualy dont get any warning liht if the egr is vacuum actuated.

Edited by 3uga on 14/06/2019 at 23:29

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - philip308s

HI, just an update, had the car looked at by a mechanic, he found that both lambada sensors are showing the same reading when theyre meant to be different? is it a faulty sensor or something else?

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - elekie&a/c doctor
Why does your mechanic think there is a problem with the lambda readings? Does he understand the operation of a wide band lambda sensor?
VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - keithd

The pre cat oxygen sensor should switch between high and low in the range 0 - 1V and the post sensor should maintain a relatively steady 0.5-0.7V at idle. I had a mini cooper with similar problems and found the post cat sensor reading was not stable. I checked for air leaks and finally replaced the pre cat sensor and this cured the stability of the post sensor and the idling and stalling problem.

Which oxygen sensor was replaced?

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - philip308s

hi, it was the pre cat sensor that i replaced, is there a way to test the sensor with a multimeter?

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - philip308s

also if i were to drive with the pre cat sensor disconnected would that help diagnose if it is the sensor?

VW FOX 1.2 2010, CHFB - 2010 VW Fox 1.2 random intermittent rough idle - elekie&a/c doctor
In answer to both your questions, no and no .