My car is lumpy/juddery early in the morning when started from cold - is this common?

[matth76 1]

Hi

Occasionally my car seems lumpy when accelarating when the car is cold, normally in the morning, for the first five minutes. It judders a very small amount for a second or two. It only occurs when I accelarate. After five minutes it accelarates fine. (By accelarate I mean up to a normal running speed - not caning it!) I told Caffyns about it a month ago when I had it serviced but they were pretty useless - they said they'd have to keep it in overnight and test it in the morning. I said no as I needed the car the next day. Anyway after they did the full service it was ok for a while...now it has returned. Any ideas what this might be...could it be the coilpack? I'm not overly bothered by it as it is always quiet and runs lovely. I suspect the new spark plugs made an improvement but the symptoms are still present.

How much would a coilpack be to get changed for a Golf VR6 at a VW dealer or independent? My car's a 1997 P-reg with 71k.

Thanks for any help.

Cheers

Matt

[Justicevr6 0]

Could be a lead that is dodgy when it is cold and has a bit of condensation on it it misses and when the engine warms the condensation evaporates and it then fires normaly.

[Nerih 0]

you know something, my car doesnt like it when its cold, it does feel a bit hesitant when when really cold, i always thought it was becuase the o2 sensor hadnt kicked in and the car was running in closed loop mode, so any large accelerations wouldnt be liked.

My car does this, i just dont accelerate very hard until she's warm, and i dont take it over 2500rpm until she's warm either....

try not to give more than 60% throttle until its warm, it'll stop the juddering.

[J5KE F 0]

me too! cutting out, juddering and more backfiring and flames then when warm! lol!

hopefully get snorted by the weekend!

[stuey 0]

My car does the same in differing amounts, normally if it is/has been damp the night before. Pretty sure mine is the coilpack. You could try it when its dark looking around the coilpack to see if there are any signs of sparking.

[VR6Pete 1,455]

check for arching on your HT leads where they connect into the coilpack!

[FishWick 21]

Yeah Nerih is right. The lambda is in closed loop (fixed at 0.5 v) for 2 minutes until the heater warms it up, so iffy running when cold is to be expected. Check your plugs for wear and oil fouling too. I recommend NGK BKR5EIX iridiums (or BKR6EIX if you're charged) as a good plug, perfect burn. available from www.sparkplugs.co.uk

Another favourite is the blue temp sender in the stat housing and also the MAF sensor, which on OBD2s is quite common, they're not as reliable as the OBD1 wire MAFS.

You can check the MAFs by hooking up a voltmeter to the red wire in the loom and making sure you get 1V at idle and 3V when you blip the throttle.

[J5KE F 0]

i think i've cooked my lambda! my air fuel gauge goes mad! but only after the 2 mins when it switches!

is there any way of testing ? the black wire is the o2 sensor/signal wire is it not?

[FishWick 21]

Yes the lambda will flick up and down rapidly on part throttle when it's heated up, that's normal. At wide open throttle the lambda is ignored and the ECU chucks in fuel from the static maps. You should see 0.7V on your A/F when booting it at full throttle.

You can check the lambda by plugging a high impeadence meter from ground to the white wire of the 02 loom and looking for a constantly fluctuating voltage. If it's stuck solid at 0.45V when it's hot, it's dead.

[J5KE F 0]

ta!

[matth76 1]

Thanks for all your replies. Sounds as though what I am experiencing is normal behaviour then. I didn't think it was that bad. I do have a new MAF sensor so that should be ok and everything runs fine after the first couple of minutes. What does the lambda sensor do exactly? Why does it stay in closed loop while cold? Does it require a certain amount of heat to operate?

[FishWick 21]

The lambda probe monitors Oxygen levels in the exhaust. Too much oxygen = weak mixture, ECU enrichens. Too little oxygen = rich, ECU weakens. That's why AF meters go mad on part throttle. They're basically showing the ECU's attempt at keeping the a/f mixture at stoich (ideal 14:1 mix). You need a very fast ECU to keep up with lambda signals and luckily Bosch M2.9 Motronic is, just, but it's slow with knock control, but that's another story.

At wide open throttle, the lambda is ignored and preset fuelling parameters kick in.

The later 4 and 5 wire 02 probes need preheating before they can accurately monitor 02 levels.....until that point (2 mins), the engine runs rich and when the Lambda kicks in (70 deg on the coolant guage) you'll feel a slight lumpiness in the idle.

[Nerih 0]

one day i want to be as smart as kevhaywire.

p.s i can tell you've had a bitching time with your charger install hehehe.