Stuttering when very cold - 1.6 Octavia SR (1u) 99

[eited02]

Bit of a strange one, This has been an ongoing issue thats now gotten worse into this winter - worsened when the temperatures have dropped to the almost 0c.

Symptoms:

First thing in the morning, partically when there has been a hard frost the car will always start. RPMS go to about 2000, drop down after a few second go to around 500 rpm, bounce up and down. The car will run rich, feel juddery, you cannot get the rpms to run steady, applying any slight amount of gas cold results on it surging to 2000-3000rpm, as soon as its warmed up and starts registering a temperature. Things will smooth out gradually. After about 5 mins it running it sounds much better and responds correctly. This is worst on frosty cold days, and on deep cold starts. If I start the car in the morning leave it for 4-5 hours it doesnt seem as bad it ONLY seems to be a major issue after its been sat cold overnight.

Secondary issue:

When the car is fully warmed up the car has a intermitant murmur very hard to notice and when your sat still at lights rpms will move around 30-40 ish and you feel the odd bump. Generally when the car or weather is warmer it is felt much less.

I suspect both these issues may be connected?

What I have tried

Had the car for 1 year, it had been sat and bearly used, so had it fully serviced, waterpump, cambelt all that stuff done.. Rocker cover had a leak, now all done.. 2 months ago the thermostat was acting lazy car did not fully warm up and would go back down to 1/3 tempreture. So this was changed... No difference..

New spark plugs fitted. No change

Throttle body cleaned with MAF sensor cleaned at the same time.. No change.

New coil pack (Boshe) fitted this week with new HT leads. (These were very old) did seem alittle better.

New o2 sensor has been fitted.

Had a re adaption done on the Throttle body and the idling issue got much better.

Whats happening Now:

Last night had a very cold night - started this morning the the main issue with it runninig rough came back dispite everything thats been done.. Once warmed up the idling issue is slighty noticable. Diffenaintly not misfiring though.

I am pretty much at a loss. there are no errors no check engine light. Do I just live with it as it is just an cold issue and will probably go away when we have better weather, it just means I have to leave her 5 minutes when we have cold weather, but I know this isnt normal ?

The MOT is due next week, which is why Ive tried my best to address these issues for emmisions purposes. Other than this issue the car is in great condition so I am releluctant to get rid. its only done 102K so not mega miles.

Any help advise appreciated?

[andburg]

Not sure sure the juddery cold starts are a fault, many modern cars are very juddery on cold starts down to fuelling and emissions control.
Some are worse than others, no idea if the 1.6 years n your car is affected by the behaviour

[eited02]

I know its a very common problem and most of the common issues happen to be Tb, Maf related when they get clogged.

I think whats happening is its misfueling until the choke ends or the o2 sensor is working - just my guess.

I have today tried disconnecting the battery. this did a reset as it now asks for radio code.

Seemed to be ok now but its been started within the day

Main problem seems to be when its first thing in the morning

[E-bmw]

eited02 said:

I have today tried disconnecting the battery. this did a reset as it now asks for radio code.

Unfortunately, this generally has zero effect on the engine management system with most cars.

You say there are no errors, what equipment has been used to scan the car as there are as many bad scanners & there are good scanners.

Have you checked the intake for splits/leaks etc?

Have you checked live data on the O2 sensor?

[eited02]

I do not have software or a scanner to hand so I am running semi blind. After the o2 sensor was changed all the codes were cleared I think the only thing was an intermittent fault on idle. Since I ve had the issues it has never actually triggered the light to go on. I had a ELM327 scanner but unfortunately did not work, the only time Ive been able to get it scanned was when the RAC came out.

I am pretty much out of ideas at the moment, so going to wait what happens with the MOT its going in tommorow, depending on how this goes it will then steer me in the direction I am going in.

I did start the car after the snow this morning and it really hated it. Sounded like it was on 3 cylinders. ECT sensor I got did not fit the car. Parts places are completely useless. Now not going to do anything until the MOT has been done.

[richhead]

might help if you said what car and engine.
i remember the old ford pinto engined cars needed a flap moving on the air filter in winter, any help?
ffs give the very nowlagable people on here a clue

[Pica-Pica]

Have you tried a tankful of top grade fuel, and a long run? That would be my first call; worth it for the £6 to £9 extra. Maybe needs a fuel system/injector clean out.

[Tony1963]

richhead said:

might help if you said what car and engine.
i remember the old ford pinto engined cars needed a flap moving on the air filter in winter, any help?
ffs give the very nowlagable people on here a clue

In the thread title

[Scrump]

Faulty temp sensor causing incorrect fuelling? I mean air temp sensor, but suppose it could also be water temp.

[cuprabob]

Might be worth changing the ECT (Engine Coolant Temp) sensor as they don't always flag a code when they fail. Cheap to replace, might not solve the issue but it will rule it out.

Have you tried unplugging the MAF to see if it runs better with it disconnected? With it unplugged you will get an EML but if it runs smoother then that can point to a faulty MAF.