1997 Passat 1.8 non turbo rough idle fault

[JHT]

Hi,
I have a passat as described above, with a very unusual fault. It idles very badly/ stalls, cuts out when cold. After running for a few minutes, it settles down and is much better. Also it failed MOT for emissions test.

There are no fault codes on vag-com.
It has a new air flow sensor
Vacume lines have been checked and split crank case breather replaced.
Throttle body has been cleaned and adaption done.
New air filter, plugs and plug leads.

I am out of ideas now. Can anyone on here help please?

[Lex Luthor]

Change the coolant temperature sensor.

[JHT]

The car certainly has symptoms of a faulty temperature sensor, but I thought that would give a fault code on Vag-com if it had failed, or is that not correct?

[Lex Luthor]

only if it is totally stuffed.
You can read the output with vagcom to test.

[JHT]

Thanks for the succestion. I found the temp sensor to be reading incorrectly because someone had replaced it with the wrong sensor in the past. Correct sensor fitted and it is running much better.

However I also took it for MOT and it failed for carbon monoxide. 0.8 where limit is 0.5.
Any suggestions?

[Lex Luthor]

Give it a really good blast up the road on the way to the retest and see if it is better.

[JHT]

I think it needs a bit more than that. It has a slight misfire when cold and the exhaust gas smells a bit even when warm- like an older less efficient car does.

The car is also fitted with LPG which I have now got working again and when on LPG, it has a destinctive misfire.
LPG always shows up faults more obviously than petrol. The slight misfire when cold turns into an obvious one all the time, so i think that is what I have to fix. It also rules out a petrol fuel system fault.

Any suggestions greatfully apreciated.

Doing a favour for a friend has turned into a nightmare, with one fault after another on this car