Other car failed emissions, anyone make sense of readings

Hope no one minds me asking a none Jimny question, just after any guidance people can offer on a car seen even less than a GEN4.

Like a few on here I have other vehicles, one is a 1994 Toyota MR2 MK2, which has failed it's MOT on emissions.

These are the results :-

Fast Idle Test
Engine speed = 2370rpm
CO = 3.07. FAIL. - MAX .30
HC = 150ppm PASS
LAMBDA = 0.928 FAIL MIN 0.970, MAX 1.030

Second Fast Idle Test
Engine speed = 2600rpm
CO = 5.03. FAIL. - MAX .30
HC = 179ppm PASS
LAMBDA = 0.852 FAIL MIN 0.970, MAX 1.030

Natural Idle Test
Engine speed = 770rpm
CO = 5.04 FAIL. - MAX .50
HC = 150ppm PASS
LAMBDA = 0.928 FAIL MIN 0.970, MAX 1.030

So the CO is off the chart but HC are within spec, but what can be concluded from these results if anything ???????

It runs and starts fine, no coughs or spluttering, no smoke etc etc.. Fully serviced, new exhaust and CAT last year and one baffled owner.

Any guidance or explanation of what the above means greatfuly accepted.

PS - The EFI predates ODB readers and the car "test mode" assumes you can drive the car on a public road, which you can't without an MOT, D'oh. Toyota did not think that one through :laugh:

Parts for the MR2 make Suzuki Jimny parts look cheap, so trying to avoid throwing my life savings at it.

The lambda is low, so it is running rich.
Check air cleaner and induction system etc.

Check temperature sensor for ecu is in spec. if it thinks it is cold it will run rich.

Does it have a Pre-cat lambda sensor? I'd look to changing this, but before you do......

These do run rich if the ecu detects it is running lean due to an exhaust leak pre lambda, check for cracked manifold, blown gasket etc.

Then fit a generic lambda sensor and hope.


If you check out an MR2 forum, someone will likely have published a test procedure that you can follow

Thank you for your feedback, it's good to know I appear to be looking at the same parts, fingers crossed..

It's a pre cat 4 wire Lambda sensor.

I have checked the temp sensor and currently have the exhaust in bits. I could not find any leaks but removed to have a look at the Lambda which is inaccessible.

Have searched the MR2 forum but not had much luck, could be that mine has the early Yamaha engine fitted, most info is on the later models.

Thanks again..

I don't think there is an exhaust leak, as the CO is high, and if the cat is working, the excess air from the leak would help get that to zero, there just isn't enough oxygen for the amount of fuel that is going in.

I'd change the lambda sensor whilst you can if it is trouble to get to anyway. The generic ones work fine.