Random lean running

I have noticed my car running really lean once or twice for a brief period then after it seems normal again.

It's done it only a couple of times and when it does it, it seems to be under light load and partial throttle.

It starts to run really crappy and when I look at my AFR gauge its leaning out badly, if I increase the the throttle it riches up and runs normal of a second but then when i go back to part throttle and light load slowly starts to lean out and loose power and run shitty?
Both times it's done this it only lasted for a short wile then seemed to go back to normal.

Maybe my fuel pump is on its way out?

I still need to change my knock sensor btw but I wouldn't of thought it would cause that would it?

It's almost asif I have a bad vac leak like a pipes come off but I know it hasn't because it's an intermittent thing   

Mine is having same issue bill. When had mine mapped i didnt realise i had a slight boost leak and a vac leak, now iv sorted these my map is out and leaning out so i need a remap. 
What ecu you running?

All stock setup at the moment mate, stock boost and everything lol

As soon as it started leaning out I suspected something had come off like a hose but then it goes away and the cars normal so I'm suspecting it's something else

Oh ok bill. Im not sure then mate, have you checked all boost pipes etc?

Not properly, I've had a quick visual inspection and all looks ok but I'll have a better look today.

I might wip the plugs out too and see if it's looking like its leaning out on any particular cylinder

Well I gave the car a quick check over today and I couldn't see anything visually out of place.

I've been out in the car today and it's been fine all day until I decided to go get some fuel from the shell garage and as soon as I left the garage and pulled onto the a38 it started to lean out really really bad, if I gave it a Bit of throttle it seamed to richen up but I didn't want to put any load on it wile it was leaning out but the lighter I went with the throttle the leaner it got and worse it ran

I pulled over right away and it was leaning out a little on idle, if I revved it with a quick sharp blip of WOT it seemed to richer up but then start slowly leaning out again. I shut her off for a few minuets but it was still leaning out when I started her again, I gave it few quick blips of wot wile stationary and it seemed to richen up and go back to normal and it was fine all the way home

What's it sounding like is the prob to you guys?

I'm thinking fuel pump or fuel pressure reg or something?
Surely I can't be a vac leak if it's intermittent, unless the stock recirc valve I have is sticking

Hi, I had intermittent lean running on mine & it turned out to be the standard ecu. I borrowed one to check & the problem vanished.

I've got a standard ecu bill

Could it be that your maf may need cleaning?

Could be the maf wiring because it's not to clever, the wires that go into the maf plug look a bit fooked.

It might be worth trying your ecu of you don't mind me pinching it for a little bit Darren

It's telling you that you need to drive it flat out then coast then flat out

Did you not have a problem with a injector on your last engine ? Maybe its coming back ?

I did have a problem with my injector on my old engine but I think that was where somebody had physically broke the tip of the injector when fitting it, before I had the car.

Its a funny old thing, I know if I go out in it now it would be fine but I would be constantly worried it will start leaning out again because it just does it without warning   

This is a random guess injector pack starting to fail. Maybe this would stall the car tho. I just adding it to see what people say

This is a hard one tbh as it could be one of many things so I would try fix all the simple things first such as any bad wiring to maf and maybe try swapping ecu and installing another fuel pump

Personally I don't think it's any of those things as this problem has come to light since you swapped the engine

I'm gonna hazard a wild guess here and say it's the throttle bodies spindle seals that have worn and is drawing in air at various positions of the throttle and the seals are leaking at certain held positions of accelerator
This would fit with the symptoms you describe so think I would swap the whole lot from old engine and put on the engine installed now

Have you done a fault code check bill just out of intrest .... if its maf its 12 iirc but maybe not show if its intermittent ..... i just trying to think as what is it it doesnt use after a certain amount of revs is it switching maps ...

Sounds like alot of wiring issues try and sort them bill as even if not now could leave you stranded or be very costley if it fails and causes damage

Bet its your ecu playing up like mine did..Easy to plug a borrowed one on to check.

Thanks for the input guys.

Bob I think you are probably right with the throttle bodie spindles leaking air but I think this random lean running I'm talking about is something else because it's a new problem that has only recently come about.

I'll try all the simple things first, I've got a couple of bits and bobs to sort out but if I can't find what's wrong with it then the whole intake plenum is getting swapped over, I just can't be bothered to do that because it looks awkward

Think you need to find someone with consult, get it plugged in and give us all the readings

buckym120 wrote:Think you need to find someone with consult, get it plugged in and give us all the readings

Yeah I think your right there buddy.


I have put guy martins ecu on   and the car doesn't seem to be any different than with my ecu but it hasn't done the running lean thing on me yet, I'm going to run it with Mr martins ecu for a bit and see if it happens again

You checked inside the ecu just incase ?
Ie took the lid off just incase someting is added or removed.
Not meaning this is your problem just interested with them adding that to the loom
Again just interested what fuse stoped the obd working ?

Jonny I forgot to have a closer look for you but I will get you some pictures today mate.

The fuse that stopped the obd working was in the fuse box by your right knee and was labeled "engine management" I replaced tat and hey presto, I can do a fault code check now lol

I couldn't get the lid off because the screws are rounded but I managed to get them all out bar 1 screw so was able to sneak a peak through the gap lol


Looks pretty standard to me.


Also can anyone tell me what this is used for?