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My 1993 LS400 is only achieving an average of 13mpg-I have noticed this for the last 4 months or so now. I have measured the economy over a few complete tank fulls of petrol.

There are no lights coming up on the dash and the car is running perfectly ok to me.

I have just had a diagnostic machine plugged in and the only error codes it shows are for the two front lambada sensors as being faulty.

When it had its mot two months ago the emissions were fine,being:

fast idle test:CO was 0.008 (Max limit for mot is 0.2)

HC was 55 (Max limit for mot is 200)

Lambada was 1.007 (Max limit for mot is 1.03)

Natural idle test CO was 0.012 ( max limit for mot is 0.300)

Do faulty sensors create poor emmissions?? When the car was mot;d it passed the test easily but I was getting poor fuel consumption at this time also?

I just phoned Lexus for a price and was quoted £199.02 for each front sensor!!

Apart from damaging my wallet by having poor mpg am I causing any damage to the car by not replacing the sensors?

Has anybody used after market sensors successfully or should they be avoided-I've seen various prices ranging from £50 to £100 but cant see what the difference in quality is?

Thanks for any advice.


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I'd take a look first at your engine temperature sender, the car may think the engine is stone cold, thereby running a rich fuel mixture. That certainly isn't good for your catalysers, which will cost a site more than a sensor or two.

Also look at obvious things, like the condition of your air filter.

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Cannot see what difference there woudl be between a 93 and a 94 car.

If its overfuelling I woudl expect you to be smelling petrol at tickover.

Mines overfuelling a bit when first started. I can smell petrol when I get out to open the gate to our yard.

Air filter would be my starting point.

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I've checked when my air filter was last changed and it was actually 4 years ago!! I've only done 11000 miles since then but obviously it is overdue a change now. I will be booking it in for a full service next week.

When the diagnostic check was done the only error codes coming up were for the front lambda sensors and no error codes came up for anything else, including the 'engine temperature sender' which Parrot of Doom suggested I should check first. Would this engine temperature sender not also show up as an error code if it was faulty?

I have now found some Lambda Sensors through Worldcarparts at £58.80 each for DENSO parts which it says are original parts and not aftermarket and a lot cheaper than quoted by Lexus.

I will book it in to have the 2 sensors changed and a full service and hopefully this will increase my MPG !!

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