Since buying the car we have experienced a couple of moments where it hesitates and feels like it is being starved of fuel for a few seconds. This clears after 20 seconds or so and things go back to normal. I already had a VAG group USB lead for my Triumph bike, so downloaded VAGCOM Lite and plugged it into the car just. The only fault that comes up is "Oxygen sensor upper" with a load of numbers and letters. Could this be the cause of the hesitation? Or is this just a knock on effect of another issue? Any tips would be much appreciated
Post up the numbers too, but it definitely sounds like a dodgy lambda sensor, which obviously is a sensor used by the ECU to determine fuelling. If the ECU is getting no info or conflicting info then the fuelling will be out of whack which could explain the occasional hesistation.
Fault is probably elsewhere, the lambda is the just first sensor the ecu has that detected the result of the misfire you mention. That vagcom lite may only read the 20 or so generic OBDII codes, so may miss the VW specific codes to help you resolve this problem. The unregistered version certainly has "limited", code reading functionality, according to ross-tech. Depending on what's wrong, the full version may not produce and better/more codes tho...
Thanks for your replies. I agree that the 'lite' version is pretty limited but i've seen similar problems on cars in the past when the lambda sensor died. Where else should I be looking? I'm thinking new plug leads, dizzy cap and rotor arm for now....
A new HT system is always a good investment on a car that old. Although the problem you describe sounds more likely to come from one of the relays, there are two main ones that can give problems. The X-contact relief relay and the fuel pump relay. You can clean them as a test to see if the problem is there or not. You can just need to remove them, open them and clean the contacts that are made when they are on. Just get some thin card/thick paper, cut a small strip, soak it in wd40, put it between the contacts, actuate the relay by pushing on the arm with you fingers, then pull the card out. It will probably be black. Repeat until it comes out clean.
could be an air leak. I've had this before when the diagnostic says lambda but it turned out to be a split hose
Thank you very much for your replies. I'll have to plug back into the car to get the full error codes and will report back. For the time being, I'm looking at giving the car a good service anyway. One thing I have found is that the plug leads aren't very tight fitting at the distributor end. They do 'click' into place but it doesn't feel like a very positive click. I'll do dizzy cap, rotor arm and leads anyway Thanks again
i have checked for air leaks as best I can and can't find anything. The oil breather hose that goes from bottom to top of the engine was split though so that now has a duct tape patch on, until i can get a new one!
That happens a lot and the one that goes to the brake servo is hard to check properly due to its position.
Thanks for the tip... I would normally have googled something like this but wondered if someone else might have had similar symptoms. Are there any known bad areas to check on the vacuum pipes?
do you know what diameter pipe they are? or are they all different? I'd go and have a look but it's chucking it down out there at the moment lol I was thinking of buying some silicon hose and replacing what i can.. Did a similar thing on my last motorbike and it made a massive difference
Well, last night I fitted new HT leads, dizzy cap and rotor arm. Also fitted a new rocker cover gasket, checked breather pipe and all vacuum pipes i could see/get to. There's no hissing or signs of vacuum leaks anywhere. Couldn't find any problems, other than the negative battery lead being a bit loose. Took the car for a short run and it didn't hesitate in a big way but still feels a bit underpowered and not silky smooth when accelerating. I've got some new sparkplugs on the way so hoping they will help a bit. I'll have a look at the relays mentioned above, but I think they may have been changed already as there are a couple of used relays and boxes in the glove box. I might try checking the timing and maybe replace the lambda sensor next (after Christmas). Can the fuel pressure regulator on the end of the fuel rail stick? The bloke we bought the car from mentioned removing and cleaning it with an air line as they can stick a bit...
It may be worth gapping the old plugs to slightly less than the official gap. If that results in an improvement, then the coil is suspect. Unless of course they have a huge gap now, then just got to normal, which would be a shame as that will be stressing you other new ignition components. I would check the relays anyway, it's easy and free and they could have been changed years ago. They, like the coil, are a weakness on the mk3.
Think I've Sussed it. Unplugged the MAF sensor earlier and took it for a spin. It was like a completely different car. It drove perfectly so have ordered a replacement (genuine VW) MAF from a breaker
Nice one! Mostly the MAF is used for changes in engine load, acceleration, etc and the lambda if used under steady state conditions. Does that describle your misfire maybe? cruising OK, misfire on acceleration... It still may not be the MAF tho. Removing the MAF puts the ECU in a safe mode, which may mask other problems..... Also, if there's a leak in that flexy consatina air pipe after the MAF, it will also be giving fasle air readings, through not fault of its own.
the problem is definitely when accelerating. It cruises along happily once up to speed. The air intake pipe is like new so no signs of any leaks along there. Fingers crossed the replacement MAF sensor sorts it out, but i am quietly confident
