Rough running & hesitation problem

[ras62]

Finally cracked what was starting to annoy me. The idle would cycle between smooth and hunting making getaway very difficult, emissions would read good then rich, then good etc etc. Small throttle openings at low revs would often result in a cough or hesitation. There didn't seem any pattern to this behavior.
I decided to send the AFM for a refurb with Frazerparts, it came back perfect, all moving parts replaced and fully tested, and while I noticed a difference when driving, the idle and hesitation problem remained. Infact they were worse. O2 sensor was suspected as the culprit even though it appeared to be working ok on the hammer, so Unit 11 changed the O2 sensor today and bingo ..the car is transformed. Perfect idle and emissions, and pulls sweet and strong from any revs. Result!!

 

[iangray100]

O2 sensors are really consumable items and in my experience should be changed every 2-4 years to keep any engine emissions running with in spec. The environment O2 sensors work in, are not conducive to long term and most testing instruments do not fully test an O2 sensor . For less than a £100 its worth just swapping it out .

 

[mcgc0]

Never really thought of it as a consumable. I guess the zirconia element must break down with heat/time etc. Read this though which might explain sluggish performance;

"Most lambda sensors will cycle from rich to lean in about 50 to 100 milliseconds, and from lean to rich in 75 to 150 milliseconds. This is referred to as the "transition time". If the O2 sensor is taking significantly longer to reverse readings, this too is an indication that it is getting sluggish and may need to be replaced. Observing the sensor's waveform on a scope is a good way to see whether or not it is slowing down with age. If the sensor becomes sluggish, it can create hesitation problems during sudden acceleration."
One for my shopping list then...

 

[ras62]

I dont think there is a definitive symptom that shows these probes are not working properly, although sluggish response is probably the most common reason offered. Mine seemed to be fine, certainly it was reading and responding ok but in fact the reading were unstable which caused all manner of strange characteristics when driving. I agree with Ian, a change every few years is recommended.