MPG and judder at idle

[Ben Cordy]

Hi all could do with a little advice. I have a 3 cylinder 1.2htp low milage which had a full cylinder head rebuild with new valves etc earlier this year (fixing the misfire issues I had).

My mpg seems to have got worse with time. Before the cylinder head work and in the 2 months after (had the work done very soon after buying) my mpg would average around high 30 low 40 mpg (calculated via fuel fill ups). The dash fuel computer would be in the high 30s low 40s for city driving and high 40 low 50 on a run or mot.

Now my average is 35 (calculated via fill ups) but it can take 15mins of driving before my display read out gets above 30 and on a run of the display rarely gets above 45. Should this be higher? Obviously it was before and it has had a full major service in the last month (the mpg was worse before the service but not a huge difference.)

Basically is this normal figures for 3 cylinder engines? What are others getting?

Also I still get a bit of juddering at idle unless the car has had a good hour plus run. Could this be related or again is it characteristic of this engine? Noticed that it didn't change even after all the work of the cylinder head rebuild.

[Lofty79]

did it have new coils and plugs/leads etc? first place for stuff like this, mpg will be down with an intermittent misfire or arcing lead/dodgy coil

[Bombbombskoda]

hi, my fab had this work done before i bought it. Yes mine is a little lumpy at first and feels like a slight misfire but gets better when warmed up, or if i give it a good rev. I have been told this engine is inherently lumpy as it is a 3 cylinder and out of balance slightly. After my first full service my MPG has settled to about 41-43 mpg (mixed driving city and gentle motorway. It improved greatly after an oil, fuel and air filter change, which hadnt been done on the previous owner sevice. Hope this helps, I think compared to new cars of its size, with small petrol engines this economy is comparable and quite good. Reading car mags has given me the impression that manufacturers claims and what the testers really get in day to day driving is very different. (my fab is same engine as yours, 03 reg, 92500 miles)

Edited 17 August, 2012 by Bombbombskoda

[Lofty79]

i was workin g on the assumption that this was outside the usual running issues you have with a 3 cylinder

[Breezy_Pete]

Does the EGR valve appear to be the factory original? (Yours is a 12-valve, right?)

Have you scanned for stored fault codes that may not yet have lit a dash warning?

How would you describe your driving style? Maybe the mpg degradation is simply that the engine is running better after the head rebuild, and so you're using it more enthusiastically?

My missus gets around 41-42 long term average, calculated, with hers. That's with mixed use, not much motorway or long journeys, but not much sitting in city traffic either, and a fairly unaggressive right foot. There seemed to be a step up of a couple of mpg when we replaced the dodgy EGR (sticking open I think).

102K on the engine, but I would say it runs very smoothly at idle, and everywhere else.

Did it get a new timing kit as it was being rebuilt?

[Ben Cordy]

Thanks for all the responses.

@Lofty79 that's exactly what I thought, misfire = poor mpg however mine seems worse following the misfire being corrected. (not immediately mpg seemed to get worse about a month or two following the misfire being fixed.)

@Bombbombskoda thanks think the juddering must just be a factor of it being a 3 cyl most seem to agree with you although your mpg seems nearer what I had when I first got the car. I assumed it was just in need of a good service but that hasn't really made much difference (did the spark plugs, oil + filter, air filter at the start of July).

@Wino mines a 6v slightly regret not getting a 12v seem to be that bit more reliable. Anyone know what the egr valve arrangement is on the 6v (if it even has one?! I :S). Didn't replace the chain when the cylinder head was done but as it only 30k miles the guys at my skoda specialist didn't feel there was any need in doing it.

[Bombbombskoda]

cheers, i have come to accept the problems weve had in common that you helped me with a while ago (economy etc) as normal.

Ps: you asked for some engine cover photos as well, I do have these and i will get them to you, been busy!

[Ben Cordy]

Yeah nature of the beast, i'll have to persuade the misses to adopt the 1.2 and ill get a vrs (in my dreams) would be great to see those pictures. Thanks for remembering!

[Breezy_Pete]

Don't think the 6v variant has EGR.

Not sure how the two variants compare on theoretical mpg, but looking at the torque/power plots, anything over 4k rpm on the 6v is pointless. Looks to have a nice bulge of torque just above idle that the 12v lacks though.

[broomy72]

mine run's a bit lumpy at idle, nature of a 3 cylinder i think, feels no worse than the 11 plate courtesy car i had a few months ago,also sound's/feel's the same as a work collegue's 09 plate,my mpg averages 38.7mpg in town use, mine only has 33k genuine miles, it does need an air filter tho,will get one next week (pay day monday) had new plugs plus oil n filter two week's ago, mine is a 6v as well

Edited 18 August, 2012 by broomy72

[Bombbombskoda]

hi freedom, god knows how to attach pics! do you have an email i can send them too?

[Bombbombskoda]

how the hell do i add pics to a message????????????????????!!!!!!!!!!!!!!!!!!!!!!!

[Lofty79]

you need to upload pics to photobucket.com and then next to picture you see an image code, you copy this and then paste it into the post, it turns to the picture once posted

[Bombbombskoda]

ta