MOT emissions fail - codes P0102 and P0171 - MAF or somethin
 

My car's been playing up for a while with the symptoms of juddering, holding back on acceleration & clearing, etc, the "usual" symptoms of the MAF / IACV units.

In addition, it gives codes P0102 and P0171 which AIUI relate to MAF issues.

I've cleaned the IACV & reset the codes but that's not resolved it.

The next step would be a replacement MAF which from reading on here I was expecting to be quite dear so I'd waited to spend on this until its MOT & this has generated just two issues, replace track rod ends (not really costly) and an emissions fail (possible financial black hole).

My concern, however, is that the garage has said, understandably that they'd need to read the codes to check what's up but have suggested an O2 sensor or a cat, but I don't believe this will be the cause of the codes & the emissions fail issue.

AIUI if I fit a working MAF the codes won't re-appear and the emissions will then be ok for the MOT, assuming of course there's nothing else causing an issue?!?!.

So my question is; would P0102 and/or P0171 indicate a worn, damaged or failing cat or 02 sensor?

It's due for a re-test next Thursday so I've got time to fit a MAF & see if this clears the codes, but didn't want to throw good money after bad if the fail had thrown up £000's of a bill.

Thanks

I'd have thought that a bad of failing O2 sensor or cat would affect running most of the time, whereas what I'm getting is very intermittent.

Have a look at these

https://youtu.be/yxXFlo-eJOY

https://youtu.be/bJRLZnjS6ms

If you have a multimeter you can do some of these tests, you don't need a scope for the basic earth and power checks.

It does sound like you have MAF issue but obviously you can't be sure that it isn't something else.

I would get the part number off the existing maf and see what matches you get online.

A genuine second hand one to compare would be ideal, and oem or new genuine would be the gold standard but having one just for testing seems overkill!

It is important that the car reaches temperature for the emissions test so the thermostat and temp sensor need to be working as well.

I would probably go after the MAF but obviously check the wiring and earths first.

My MAF for the 1.9D was £15 from a local breakers and works perfectly, new aftermarket ones are around £80, so guessing it's similar pricing for petrols?

Unfortunately, I've just tried a spare MAF from a breakers and the problems still there (lumpy running on & off, poor tickover & the same two codes appearing).

I'm concerned that when the car goes into the garage when they attempt to resolve the issue next week, that they'll get involved in a 'swap this, then this, then this ...' method, with me left picking up the bill for a lot of components that don't cure the issue.

Could be cheaper & quicker to simply let it go to the car garage in the sky ... Mr Salvage ... and put my cash into another car instead.

Morning , the quickest solution & the right one is a live data read of the engine at working temp after a run . Watching the data from the sensors tells you what is causing your errors . It is not unusual for one failing sensor to force another sensor to work outside it's programmed limits and that triggers codes incorrectly

You could also ask your MOT station if they can do an emission test to see exactly what reading the gas analyser is sampling . Faulty Lambda gives readings that wander all over the place , a failed cat will typically hold a steady CO value

We often perform this for customers who have failed emission tests , after repairs have been made

Before you leap into big money spending , check plug gaps , coil packs are fitted tight / wiring to coil pack is good / clean / secure

Taking data from the MOT test we have

Fast idle test
CO = 0.97 Not Ok
HC = 151 Ok
Lamba 0.994 Ok

Second fast idle test
CO = 0.13 Ok
HC = 62 Ok
Lambda = 1.102 Not ok

Natural idle test
CO = 5.656 Not ok

As mentioned I swapped the MAF with one from a volvo breakers and that seems a little better but the problem's not cured.

To assume that MAF was at fault too ... unlikely.

I've tried cleaning the IACV more than once but again that's only seemed to cure it temporarily, which could have simply been down to luck.

The symptoms are, lumpy running sometimes, that 'flat spot' feeling as if your pressing of the pedal's not being ignored by the fuel system and also the running on of the fan when switching off the engine. The fan issue can be overcome, most times, by starting the car, letting it run for about 10 sec & then switching it off again.

All seem to be MAF related from what I've read on here but it's all supposition really without actual data & I don't fancy paying for parts to be replaced because they 'should' cure the problem.

Thanks for the vids, will take a look shortly.

And yes, I checked the replacment MAF's codes and it's an exact match for the one I've got.

You may need to reset the codes with the replacement maf.

With the high CO I would believe that either the engine is not hot enough (thermostat?), temp sensor faulty, the maf is faulty (or wiring), O2 sensor faulty.

As someone else said, you really need to see live data readouts for these items.

I think the diagnosis you need may be beyond your average garage who just read codes and replace parts.

Maybe try an engine tuner or someone who actually understands how all the components work together.

The advice on spark plugs and coil packs is also something to look at. It'll never run right if the spark plugs are worn out.

Morning again , looking at those values , I would aim my suspicions at one or both of the lambda sensors & possibly a leak in the exhaust . Again I strongly recommend a live data read to make sure ALL engine values are as they should be