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Excessive fuel consumption and lumpy when restarted warm


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Hi Guys,


I'm new here - hope you don't mind me posting a question straight away!!


Bought a 1998 2.0l outback about 2 months ago and I'm having a problem with very lumpy running when I restart the car when it is warm. 


Starting from cold the car runs great, no problem at all. When you stop and leave the car for any time and then restart, the car doesn't want to pick up, and it's like it is on 2 cylinders.


It does eventually clear and run normally, but as we mainly use it around our small town, it doesn't get a chance to clear, especially as theres a lot of slow running.


Also, just filled it up after 100km and put in 21 litres, which is a bit steep, even for running around town!


When I bought the car there was an overheating problem too, but I fixed that with a new rad.


Any advice anyone could offer would be great. As I'm in a remote part of Spain, I'd have to drive about 70 miles to find a dealer, so if there is any way I could narrow it down a bit first, that would be great.


I've attached a picture of the coil/manifold and the vin.


Thanks in advance!



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Hi, first things first ...


when was it last serviced ?


Air filter, pollen filter fuel filter  oil etc?  


Have you checked the ecu for any fault codes?    ( can you do a blink code check)    -   what codes are returned?



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HI Mart


Thanks for the reply


I did a service when I bought it, and the filters are all now good. Changed the auto box filter and oil too, as we thought it was that at first, with overheating auto oil, until the rad was renewed and the engine overheating problem was then fixed.


Haven't done a blink check. I'll have a go at that sometime over the weekend and get back to you.


Any ideas from what you've read so far?



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Ok if ive worked it out correctly it comes back as  about 2mpg


thats not good,  your running very rich, what colour is the exhaust smoke?   


When was the last time you changed your plugs?  


will the car pull above 3K,  it sounds as if the car is over fuelling to keep things happy .


you need to get it sorted soon or you could damage the cats


I'll do some more digging around



One other is it a turbo or NA model



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BTW  this is done at your own risk,  i'm only providing links to other sites ...


Have a look at this..


If you dont feel capable or happy doing it yourself,  have it carried out by someone compitent





see if you can get your blink codes ..


Or if you have an  OBDII reader plug that in and see what it returns




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Doing some digging has come up with


Engine temp sensor or MAF 


does the car get up to temp normally, or is it running cold?


a failed or failing sensor will tell the car its cold (when its actually hot), and keep sending  more fuel into the sytem to get the car up to temp


Alternativly the MAF can do that too,


Have you got a friend with the same car, you can do a swap of parts, and see if it makes a difference


I would check connections to the engine temp sensor and maf to make sure they  good, no broken wires etc. 


alos check your fues boxes for duff fuses



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Hi Mart


Thanks for all that.


It's not got a turbo.


It pulls above 3k fine, once it gets over the low end lumpyness. Haven't changed the plugs. exhaust smoke seems normal, but you can smell the petrol when you start it up from hot. Then,

the lumpyness cures itself if you drive more than four or so miles and aren't in stop start traffic.


So the really bad fuel economy isn't helped by all the stop start we do, as each time it stops, on restart it is doing what you say - over fuelling.

When the car starts from cold and isn't stopped it runs fine the whole time.  Gets up to temp ok and the fans cut in correctly.


Don't know anyone else who has the same car, so swapping out isn't an option.


I'll check everything as you say, and I'll have a go at the blink code check too.


Thanks again Mart - appreciate it.



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Hi Mart,


I have checked the fuses and connections under the bonnet and all seems ok, apart from that there may be a 30A fuse missing. I have attached a photo, and it seems SBF No8 fuse is not there? Is that one important/anything to do with the problem please?


RE the blink test for ecu codes, I don't feel confident enough to do it myself, so I have a mechanic friend who is coming round over the weekend hopefully, to do that and get an error code if poss.


My mechanic friend has asked me a couple of questions to ask you if that's ok.


Where is the MAF sensor and how do we recognise it?


Is the engine temp sensor the same as the one feeding the dash guage, or a different one, and where is it please?


Thank you for your help.



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Hi Mick,

To find your MAF...

From comparing your picture & the manual

2.0 - is at the back of the engine slap bang in the middle, it bolts directly onto the 4 branch air intake

The electrical connector on the front is for the air intake temp sensor... i will see if i can locate your maf for this model shortly

Not sure of the engine temp sensor, but yes it is the one which feeds the dash display , let me grab my worksop manuals and have a gander


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I need a wide view shot of your engine bay please Mick,

Looking at the workshop manual for the 2003 outback / leggy

2.0 Type 1 has an MAP / temp sensor mounted in the inlet manifold, with an airbox feeding direct.

2.0 Type 2 has a side mounted airbox and a maf built in

looking at your picture, you have the type one airbox, but no MAP sensor in the manifold...

hence my request for some more pics


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Right from what i can work out ..

You dont have a MAF, but a combination of intake air temp sensor & MAP (manifold absolute prressure) sensor.

Coupled with the engine temp sensor give the 3 parameters for controlling the fuel ratio

looking at the picture the inlet air temp is easy to spot. the MAP though can be several places, depending on what model / country

looking at my worksop manual for the 2003 its either in the manifold or throttle body.

The one that looks like the right one i have circled, although i could be wrong.


I cant see where your engine temp sensor is located , as the manual is vague, ... its usuially just a plug going directly into the engine block

Not sure how you clean an air temp sensor, (normally its a MAF)

My map sensor, i just sprayed with brake cleaner and shook off excess and left to dry.

Engine temp sensor is just a replacement

in terms of replacement prices ... Main dealer guestimates - £100+ for the MAP £100+ for the air sensor & £50 for the engine temps sensor

I cant find anything listed for your car in terms of Pattern parts here in blighty

You need to get it to a garage for some diagnositicery


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Hi Mart


Thank you so much for the help and all the advice - I really appreciate it.


I am waiting on a guy to put it on his computer. He's just a very busy fellow here as there's no one else for miles!


With the heat here now, it's playing up all the time, but can be driven as long as you keep the revs above 2,000. 



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Ok, it's been on a diagnostic finally.


The Engine Management light was missing too, so the fault has been on it for a while, and was on the car when I bought it..


The computer said  'Knock Sensor Bank 1 Left'


Upon closer inspection, Plug 1 plughole was full up with oil, and plug 2 was arcing.


With the arcing plug replaced, and the oil drained from the spark plug hole, the fault has gone and the car is fine, and the fault code has not come back.


I have been told that the ECU changed the mixture to compensate for the error, which is where the heavy fuel consumption came in.


Only things to do are replace all spark plugs and deal with the oil leaking and immersing the spark plug. 


Can anyone help please, and tell me what actually seals the spark plug holes from oil ingress? and what is involved with fixing the problem?


I'd forgotten how nice the car is to drive without a fault!!


Thank you for your help, in advance.



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