This one has me stumped.
Recently my car has bern idling a little rough in the morning while cold - only while cold.
No big deal, its always been a little rough, however when I change into reverse, the car idles really rough, dropping to around 200rpm at which point it either stalls or chokes back to 600 rpm then either repeats the process or stabilises at 900rpm.

I initially thought it was a battery issue as the interior light flickers while it idles.
Checking the battery though, I get 12volts at crankover, which then builds up to 14.8v in about five seconds

So, ruling out the battery, I next thought maybe its the air intake as I only just put a new air filter on two weeks prior.
No luck, everything was clean and clear.

Maybe it was a loose or cracked vacuum hose - again, no dice, lines were all good.

This problem started and gradually got worse when my mechanic - without my requesting it - serviced and tuned my throttle body at 300,000kms, though when it first started, it was the opposite - the car idled too high (1250rpm) while warm

So I checked the throttle body. Cleaned it and put it back together, nothing. Still doing it.

The only thing left I can think of is the automatic choke, but I don't know anything about that.
The car runs perfect when in drive, even if cold, and theres no problems with reverse once the car has warmed up.

Anybody got any tips / ideas?


One other little strange thing is that once every few months, just randomly, while the car is idling, the speedometer will fluctuate between 0 and 20 km/h depending on the exact idle speed - even though I am stationary.
After driving a few kms I guess it fixes it as I don't see it again for a few weeks to months

didn't the V8 in the earlier EF/EL have a function that they limit engine torque significantly in reverse to protect the transmission. possible this function still exists in the later models. this may be why it looses power/ torque in reverse. but if it runs rough might have to get that sorted first. maybe try removing the inhibitor switch and trick it into thinking its in drive but really in reverse, see what this does.

Could be the O2 sensors - My AU did this but also in Drive until the ECU failed it every morning.

Once of my sensors was intermittent - heat related.

Nigel

I'm leaning toward O2 sensor as well.
After removing a section of muffler from my exhaust, the car is idling far better, but is still slightly choking this time when I first accellerate in reverse. Far better than it was before though.

Before we go blaming the exhaust, I can say I doubt it was related to that.
The exhaust was only 10 months old or so and was a straight-through sports exhaust. There were no blockages or even carbon deposits.

Try disconnecting the o2 sensors. That at least will give you a consistent result. The Eau should fail them fairly quickly

Did you manage to get this issue sorted and what was it?

I am experiencing a similar problem with idling myself and want to eliminate other issues before I change the "automatic choke" part

Cheers Paul

Forgot my password for a few days there...


Anyway, the issue turned out to be the O2 sensor inside the air intake. A thorough cleaning fixed the issue but I notice it coming back slightly after a few months. I might see if I can get a new one.

So is that the maf or temp sensor you cleaned

Ait is in the intake pipe(air intake temp) maf(mass airflow) is bolted to the air box.
Id try cleaning the maf and t/b as well if not already done and give it a dose of intake/combustion cleaner,make sure your filter isn't over oiled if its a k and n.