Help! Mot Failure

[J&A]

Hi,

Took my MR2 (1994 Rev.3 N/A Non-Import) in for its' MOT yesterday, and was really disappointed that it failed- on one item, the emissions test. TBH I've noticed for some time that, once warm the engine suffers from a slight misfire on tickover, and at higher RPM in no-load conditions. Strangely enough the car exhibited similar symptoms at last years test.

On that occasion I was told that it was ignition based. I therefore fitted new plugs (Denso Platinum), HT Leads (Magnecor) and rotor arm/Dizzy cap (Blueprint), and sure enough it flew through the retest. This time tho the guy who conducted the test (Workshop foreman in Toyota dealership prior to his present job) reckoned that the electrics were sound, advising that it could be a knackered cat (Fitted new along with stainless back box 14 months ago), oil in the gases, broken lambda sensor or even a faulty/leaky injector (Please God, not that!).

The misfire is uneven, and sounds more like a cylinder intermittently missing- giving a "chuffing" sound. The degree of missing seems to vary depending upon the revs-it will be really noticeable at 1000 rpm, disappear at 2000 but reappear at 3000. Sods' law, it seems particularly bad at the MOTs Natural & Fast Idle settings- hence the failure. However, once the car is underway the burbling disappears and the car pulls strongly up to the red line in lower gears. Totally mystifying, and not a little frustrating.

With virtually all the ignition components replaced I really have no idea where to look next. I've found a guy who specialises in jap diagnostics so I'm hoping that he'll be able to find an easy workaround, but in the meantime any observations or advice would be gratefully received. Thanks

PS: For the sake of completeness I've included the gases printout:

1st Fast Idle:

CO 0.82%vol (Limit <0.30%- FAIL)

HC 299ppm (Limit <200ppm- FAIL)

Lambda 1.014 (Limit 0.970-1.030- PASS)

2nd Fast Idle:

CO 0.78%vol (Limit <0.30%- FAIL)

HC 190ppm vol (Limit <200ppm vol- PASS)

Lambda 1.004 (Limit 0.970-1.030- PASS)

Natural Idle (750 rpm)

CO 0.74% vol (Limit <0.50% vol- FAIL)

If you need any further info please let me know. Thanks.

[blz-8027]

Hi,

Took my MR2 (1994 Rev.3 N/A Non-Import) in for its' MOT yesterday, and was really disappointed that it failed- on one item, the emissions test. TBH I've noticed for some time that, once warm the engine suffers from a slight misfire on tickover, and at higher RPM in no-load conditions. Strangely enough the car exhibited similar symptoms at last years test.

On that occasion I was told that it was ignition based. I therefore fitted new plugs (Denso Platinum), HT Leads (Magnecor) and rotor arm/Dizzy cap (Blueprint), and sure enough it flew through the retest. This time tho the guy who conducted the test (Workshop foreman in Toyota dealership prior to his present job) reckoned that the electrics were sound, advising that it could be a knackered cat (Fitted new along with stainless back box 14 months ago), oil in the gases, broken lambda sensor or even a faulty/leaky injector (Please God, not that!).

The misfire is uneven, and sounds more like a cylinder intermittently missing- giving a "chuffing" sound. The degree of missing seems to vary depending upon the revs-it will be really noticeable at 1000 rpm, disappear at 2000 but reappear at 3000. Sods' law, it seems particularly bad at the MOTs Natural & Fast Idle settings- hence the failure. However, once the car is underway the burbling disappears and the car pulls strongly up to the red line in lower gears. Totally mystifying, and not a little frustrating.

With virtually all the ignition components replaced I really have no idea where to look next. I've found a guy who specialises in jap diagnostics so I'm hoping that he'll be able to find an easy workaround, but in the meantime any observations or advice would be gratefully received. Thanks

PS: For the sake of completeness I've included the gases printout:

1st Fast Idle:

CO 0.82%vol (Limit <0.30%- FAIL)

HC 299ppm (Limit <200ppm- FAIL)

Lambda 1.014 (Limit 0.970-1.030- PASS)

2nd Fast Idle:

CO 0.78%vol (Limit <0.30%- FAIL)

HC 190ppm vol (Limit <200ppm vol- PASS)

Lambda 1.004 (Limit 0.970-1.030- PASS)

Natural Idle (750 rpm)

CO 0.74% vol (Limit <0.50% vol- FAIL)

If you need any further info please let me know. Thanks.

Ive just took a 1994 UK N/A for test for a mate ,That also failed on the emissions (Co2)

garage didnt know what to look at so couldnt advise what to look for ,said it might be the lamda needs cleaning

changed the oil removed the airfilter and it flew through the retest ,but still dont know what caused it to fail