had a little problem with an aceleration hesitation at low revs while cold.
anyway today start car up in the garrage and engine smelt really rich.
when my car was at the tuners he said the AFRs were fine, (Not at idle)
now could my problems be related to a faulty 02?
if im correct, the o2 sensor only is used during closed loop mode under idle and low load
resulting in rich/rough idle that wouldnt have been discovered during tuning, as its in open loop.
and also causing hesitation due to the really rich mixture at low rpms when the car is still cold?

lol. O2 sensor doesn't come into play at idle or low rpm, you got that back to front.

ANY car started up in an enclosed space will smell rich, even a new one. lol Lots of raw fuel gets pumped out the back when the engine is cold. A car started on gas might be a different story.

i had a mate sitting behind me at the lights and he said it smelt rich too

lol. O2 sensor doesn't come into play at idle or low rpm, you got that back to front.

Sorry, that's not correct.

When the engine coolant is below a certain temperature (not sure of exact value, but probably 60-70C), the ECU ignores the O2 sensor.

Once the coolant temp rises beyond that (and it will normally stabilise at 95-100C), the ECU uses the O2 sensor to adjust the fuelling except at very high revs (6000+) or very high loads (75% typically, but drops a bit as revs rise towards 6000). With a warm engine, the O2 sensor is very definitely being used at idle.

From my experience with Moristech ECU and AFR Gauge I support this statement.

Reason for rich idle-only AFR wouldn't necessary be the (faulty) oxy sensor, cos it would run out of whack at other revs/load too.
It's not very difficult to actually test the oxy - provided you have repair book handy.
Without further knowledge on your situation - what does the guy (tuner?), mean when he said AFRs are ok? Was it dynoed etc? What AFR readings did you get? These donks run surprisinlgy lean on cruise mode....

when the car was doing a power run, on the dyno. he looked at the AFR's and said he wouldnt go any leaner, as it was running fairly lean as it was.
my issue is that its running rich at idle, and sometimes hesitates when accelerating on cold mornings. within the first 5 mins of running.

Can't see in your Profile that you would have an Interceptor ECU to adjust idle - or any - AFR. So dunno how to do it on std ECU situation. Considering all other RPM AFR is ok as stated. He didn't give you figures???


when the car was doing a power run, on the dyno. he looked at the AFR's and said he wouldnt go any leaner, as it was running fairly lean as it was.
my issue is that its running rich at idle, and sometimes hesitates when accelerating on cold mornings. within the first 5 mins of running.

i have a morristech prosequential piggy ecu.
but changing the figs on that would only work when the stock ECU is using its map. not the 02 sensor.
the tuner did have the figs, but ive misplaced the graph.
but he did say that its running fairly lean, and that he didnt reccommend going any leaner.