How to lean the fuel mixture on mk4 golf gti

assuning there is nothing major wrong, get some forte injector and use it as recommended. I once had a renault laguna diesel fail an MOT test, a roadworthiness test that is, on emissions...it was absolutely chucking out black smoke but the engine ran well. I put 2 bottles of injector cleaner in the half full tank and went out for an eighty mile drive revving the engine in the lower gears. I returned to the testing station an hour and a half later and the engine was running perfectly.
Alternatively, assuming the engine runs well but is just a little smokey, have it terracleaned, this will remove most of the carbon deposits from the engine/exhaust and should increase the life of your engine simultaneously improving fuel economy

Can't by pass as oxygen sensors control your fuel

I suspect your exhaust converter has failed & the car has
been running rich for years & ruined it

Wouldn't your repair guy be able to solve all your issues,
after all you were at a shop for some work

Sounds like they sold some service instead of diagnosing
the reason you were there

didnt know that the earlier golfs had two lambda sensors,but that said,if there are supposed to be two,then there will be one before the catalytic convertor (pre-cat)and then one after,if the car has had the exhaust changed by a previous owner,then this maybe the issue,you need to get it checked out because this is an MOT faliure item,i.e emissions too high/hydrocarbons too high.seems the cheapest way to solve this is by fitting the correct exhaust unfortunately.hope this helps

Will probably be the MAF sensor or the Lamda sensor. Is there a lack of power on acceleration?

re the funny smell, i need to speak to my friend as i have never heard of that one,does it smell of rotten eggs???

hi the MAF is more than likley to produce the wrong fuel to air mix, all the lamda realy does is keep an eye on the burnt fuel deposites and then sends the signal back to the ecu, which in turn then opens or closes the mixture , but if it is sending the correct signal and the MAF is not reading it right this will in turn cause your system to run either lean or rich, it may actually not be faulty as such , as it is still working according to the ecu so you wont get any error codes hope that helps sorta

The advice that the garage gave you seems right. If any bushes were worn they would show up on the MOT Test. Try taking it to another garage to check out the Cat for your peace of mind.

If you facing a little black smoke along with it your engine is running a little rich. Black smoke indicates unburned fuel and this could cause a black stain and leading to test failure

ive bought a cat back scorpion exhaust for my mk4 2.0 golf gti the problem is its banging off the bottom off the car witch is doing my nut in i bought a 4motion rear valance for the cut out for the tail pipe witch was a waist of time as the exhaust is no where near the cut out as it will not go any higher because its already hitting the body does any one else have this problem your advice on this would be helpfull thanks

Buy a new one muppet.