W Reg Vvti, Recurring "fuel Mix Too Lean" Error Code

[spikit]

Hi friendly folks,

I have a W reg Yaris Automatic VVTI 1.3 which has done 100k and has started coming up with an engine malfunction light. I've reset it several times but it keeps coming back.

My cheapo OBDII reader shows it's a "Fuel mix too lean" code, which has been confirmed by the local garage. They have looked at the live output from the sensors (whilst idling) and determined that, in the main, everything is doing as it should. However they recon it would cost a bomb to investigate fully. The problem seems to be only an instantaneous/intermittent one, which seems to occur more often in hot weather and when the car is being revved relatively hard (i.e. to get onto a main road from a slip road) and particularly when the car is started from warm (i.e. after stopping and driving off from a petrol station). I use a mix of garages for fuels, and have never tried any of the high octane varieties.

I have taken off the MAF sensor and given it a good soak/shake in alcohol (IPA). It looks intact and not grubby at all. I've also cleaned and wiggled the wiring harnesses to it.

Just wondering if anyone had any good ideas to try before getting it thoroughly checked at great cost? Cleaning additive has been suggested; would that make any difference? Would it be worth buying a new MAF myself and giving that a go? Alternatively, given the age, is it worth just keeping an eye on the frequency of occurrances and running the car into the ground; hoping that it doesn't come up during the MOTs? Sounds wrong, but if it really is only an instantaneous fault.....

I'd really appreciate any ideas.

Many thanks in advance for your help,

T

[Cookie-monster]

Last time I got that error code on a Nissan Primera, and it was the MAF sensor that was on its way out - they are only good for about 100K, and if the cleaning does not work, and you get the same error code again then its time for a new MAF - they are not cheap for OE but you can get them on eBay for £40-£70 mark. The other symptoms of a failing MAF are erratic idle, which eventually causes stalling, and intermittent power drop out whilst driving. As the MAF goes out of range, it makes the ECU think it is getting less air intake than it actually is, so it leans out the mixture, but this in turn gets an unexpected response from the Lambda sensor in the exhaust, so it gets confused and switches on the Managemnet light and stores the "mixtur too lean" code.

[spikit]

Thanks CM, much appreciated.

Haven't had any other symptoms at all.

I'll give a new MAF from eBay a go; even if it turns out not to be that, I won't be disappointed for £40.

Cheers

[Cookie-monster]

Before you do change the MAF - its worth checking that all the vacuum pipes such as the emmissions canister solenoid (mounted on the right hand side of the air cleaner housing) to inlet manifold and the brake servo vac pipe are secure and not leaking as this will lean out the mixture too - in fact, any vacuum leaks from the air cleaner where the MAF is located to the cylinder intakes could cuase problems so check for any hissing or suspected leaks around the inlet manifold while the engine is idling.

Just to check - when you remove the maf, there is a small bulb on the side of it that you may think is the part to be cleaned - this is only the air intake temp sensor, the actual wires that need cleaning are up inside the ducting , and you will only see them if the maf is held up to the light and you look up the plastic channel - there are 2 small wires that look like tiny light bulb filaments that need to be soaked in cleaner - I used tape head cleaner solution and a small cotton bud to reach up to them - but take care not to damage them as they are fragile.

[spikit]

Thanks for all the advice CM.

I haven't been able to locate any leaks, and yes, I (think I) was cleaning the correct part. I didn't actually touch the filaments, I just immersed the whole assembly in IPA, shook it and left it overnight to soak.

I've got a cheapo aftermarket MAF now from eBay (no markings). I've fitted it and had a good drive; the engine warning light doesn't seem to have come back yet, so (fingers crossed) this has solved the problem. However, the car now suffers irregular idling speeds (it seems lower than before) and threatens to stall. A quick google shows this to be quite a common problem. I've unplugged the Battery for an hour to reset the ECU. Do you happen to know if the ECU will "calibrate" to the new MAF in due course, or will this problem continue?

Now that I'm fairly sure that the MAF was the problem, I'd be happy to buy a proper OEM replacement if anyone could convince me that the idling problem would go away?

Cheers