I have an Au3 - 2002 on petrol.

It will idle fine when it first starts up.
Once it gets warm after 5 or so KM it starts to idle really rough.
Its not as rough if the air con is on.

I have replaced the spark plugs. This made a little bit of a difference.

Anyone got any more ideas ?

I have the exact same problem. Its driving me nuts!!!
I have replaced the crank angle sensor, coil pack, and fuel pump as per the PCM codes. No difference.
I also have replaced both inlet and exhaust gaskets, no air leaks. Still rough.
I have cleaned the throttle body and IAC valve. Still rough!!!
It has brand new plugs (correct gap) and MSD superconductor leads, new K&N air filter and XR8 Intake.
The fact is, I'm sick of throwing money at it, the problem is still there.
Its weird cause when the AirCon is on, the idle is as smooth as silk. I even thought my car had stalled at the lights its that smooth!!!
I feel your pain as I am at my wits end to try and diagnose this.
I was told to check all earth points as the PCM is sensitive to voltage fluctuations, will do this on the weekend.
Fingers crossed eh??
If anyone has any ideas it would be greatly appreciated.
If anyone knows how to fix this I will buy them a slab, bugger it 2 slabs of whatever you drink.
Brett

oxygen sensor

Tried another one same result.

I am thinking air flow sensor or plug leads atm.

Is there a way to set base timmming on AU's or don't they need it since they auto time?

Hi Mate,

Your problem sounds exactly like the one I had and I tried everything you have done and prpbably more and could not find the problem at all. My mechanic and I after endless hours on the car and the forums decided not to worry about it for a while and wait for something more noticable to show. One day it really annoyed me and I had a real good look around the motor and noticed some coolant stain from leaking between the head and the block. Even though the car only had 75000kms on it we decided to do the head and a few slight mods while we were there and not a problem since. So sorry mate but I have a feeling its your head gasket.

clean the fuel press regulator

clean the fuel press regulator

Hi Mate,

Your problem sounds exactly like the one I had and I tried everything you have done and prpbably more and could not find the problem at all. My mechanic and I after endless hours on the car and the forums decided not to worry about it for a while and wait for something more noticable to show. One day it really annoyed me and I had a real good look around the motor and noticed some coolant stain from leaking between the head and the block. Even though the car only had 75000kms on it we decided to do the head and a few slight mods while we were there and not a problem since. So sorry mate but I have a feeling its your head gasket.


I forgot to mention that. I have had the head tested twice by 2 different ford dealers. No problems there. In fact, that was the first thing I thought too but its not that.
I put a scan tool on it again and now there is a PCM ROM code fault. Faulty PCM?? Or maybe its not getting a clean voltage i.e. check earth cables. I hope its something simple like that.

It was the intake manifold gasket.

It had a crack in it.
Replaced it and everything is fine.

But its done another intake manifold gasket. Seems to do them if you go on a drive for more than 2 hours with the air con on.

i had similar problems but after going through your scenario the last thing i done was coil pack and fuel filter and rough idle was gone

Get yourself a can of carby cleaner ($6) and spray the outside of the inlet manifold where it goes into the head, each inlet tract at a time, if the engine coughs, picks up, idles better, worse, or runs differently, then you have a leaking inlet manifold - for $40 (price of the gasket -easy to fit) I'd try there first. AU's are notorious for it, my ute had it - sounded like it was running on 3 cylinders at idle and was 'ok' when it had some more fuel flowing - choke on or when the A/C kicked in, or I was cruising at 60 in 4th... Just a suggestion...