The readings were many times over the limit.

I've replaced the air filter and checked the condition of the spark plugs which are normal. I'm going to completely clean the MAF for deposits.

What other area(s) should I also look into to bring down the CO emissions? TIA.

 

If it were mine I would change the oxygen sensors ..evidently there is a hole in the footwell to get access through the fire wall

 

What's interesting about your figures is your lambda reading is low (it wouldn't fail a UK MOT on that value), but the CO readings are 10x what they should be and HC is 0. You can check what the car thinks the Lambda readings are if you have Torque or DashCommand and see if they match the reading they got at your exhaust pipe, which would give you a clue as to where the problem is. I keep the printouts from the annual emission tests for future reference - if you have your old ones you could have a look to see what has changed.

If you do go the route of changing the O2 sensors, make sure you get the right ones for your car, as they changed over the years, and don't be tempted by cheap clones, get a good brand from a reputable supplier.

 

I don't even know if the 97s had PVC valves in your country or any country, but the 1 and only time I failed for CO (different car, pre 1997) it was a failed PVC valve.

Friend I've no idea if this can be bridged into something useful for you, but shared as a data point.

We must have some sort of positive crankcase ventilation (?).

I hope you nail it with something easy.

John

 

What are the fuel trims (LTFTs & STFTs, hot engine, parked) at idle and then again at about 2500rpm?

Also, is it running CL (closed loop)?

It's quite possible you have something such as dirty MAF.

 

Shall we assume the Check Engine Light is off and there are no codes to report? Air filter is step in the right direction.

If you have an ODBII scanner, it won't cost anything to synch the ECM with the Throttle Position Sensor. Look for "TPS and PPS adjustment via OBD" in this forum. Jot down as much information off the scanner before making changes so you can identify some readings out of spec first off, compare readings afterwards and have data to fall back on, like throttle position at startup and after warmup, idle rpms, fuel trims, water & air temperature, voltage, fuel pressure if available, MAF, etc... You may want to post some of the data here for comments. If you do a hard reset, you'll need to put some miles on the Jag so the ECM can relearn it's parameters.

 

After considering all solutions suggested by fellow members of this forum and local car repair experts, I decided to add one bottle (~400ml) of STP Ultra 5 In 1 Fuel System Cleaner to a full tank of gas to clean up the engine. After using up the tank of gas I took it back for a re-inspection. The CO passing grade for idle is 0.5% and for fast idle is 0.3%. The passing mark was still exceeded, but it had come down VERY SIGNIFICANTLY from the first test 12 days ago to just exceeding the mark by only about 35%. So I poured in another bottle of STP to another full tank of gas and ran it for another 50 miles at high revs and took it in the next day for another re-test, and lo and behold it passed the test as shown in the report posted above.

I must admit I've no trust in fuel additives and have never in my entire life used any, but this episode has completely changed my view on fuel additives which I now swear by it.

To recount the whole story of why I got into this HIGH CO emissions saga, 2 weeks before my first annual inspection test, I ran into the very common "restricted performance" warning which didn't allow me to rev the engine any higher than something like 1.200 rpm. That was finally diagnosed as a Ground Fault/Failure of the TPS (Throttle Position Sensor) connector which was cured by simply tapping/hammering the body of the TPS connector. But driving under the "restricted performance" condition for 2 weeks caused significant engine clog up which was finally cleared up by using the STP treatment rather than a very expensive Catalytic Converter replacement.

Cheers and a Very Happy Year of the Rabbit to ALL!