318is rough idle

[Binkerment]

Hi Guys,

Looking for info on what could be a rough idle issue.
Car starts and for the fist few seconds hunts and more often than not, cut out. Bare in mind it's sat all winter in the garage with the odd start here and there, so could just be needing a good run.
The idle does sound a little lumpy though. The rev counter doesn't seem to move so it can't be hunting too much, just lumpy if anything with the usual strong smell of fuel.
Once warm the lumpy idle is still there. The car pulls strong right through the revs with no issue.
I went a run last year and a guy in the group behind me reckoned he could smell fuel as though its running rich.
Also, I end up with the white paint yellowing around the back end with exhaust fumes.
Not really checked much so far.
Any ideas where to start?

[rix313]

The usual stuff of chancing for air leaks is a good place to start. It is possible that in its life some bright spark has faffed around with the AFM trying to make more POWAH by messing around with it. Be worth taking it somewhere with a gas analyser and checking it and adjusting it if required. Also how old is the fuel?

[Binkerment]

The usual stuff of chancing for air leaks is a good place to start. It is possible that in its life some bright spark has faffed around with the AFM trying to make more POWAH by messing around with it. Be worth taking it somewhere with a gas analyser and checking it and adjusting it if required. Also how old is the fuel?

The fuel will be quite old. Last September it was filled but it was doing it back then as well.is there any way of messing with the fuel air mix??

[Binkerment]

The usual stuff of chancing for air leaks is a good place to start. It is possible that in its life some bright spark has faffed around with the AFM trying to make more POWAH by messing around with it. Be worth taking it somewhere with a gas analyser and checking it and adjusting it if required. Also how old is the fuel?

Should the engine rpm be slightly higher when cold??

[Binkerment]

Update.
I removed the idle control valve and on refitting, applied some sealant around the bottom fitting on the ICV and some on the hose that comes off the ICV where it goes on to the engine.
I also added some to the small hose that comes off the underside of the AFM.
Now the car fires up and immediately raises idle speed to around 3k. It sits steady and doesn't hunt. Could this now be because the AFM is out of adjustment and its over fuelling??

[tha881]

Not sure how it is idling at 3k rpms. Maybe an air leak somewhere.

It might be worth getting brand new injectors. They are the part that delivers the fuel directly into the engine. If it is overfueling one or more could be stuck open or even slowly leaking once switched off.

A quick test would be to remove the fuel pump relay and start it till it dies. Leave the car a few hours before refitting the relay and then starting immediately with the turn of the key, and see if the idle is a bit smoother.

Does the oil smell of fuel? If so you will want to change that, if can thin out and not offer full protection, which can also cause a poor idle.

[Binkerment]

But it's only started doing it right after I sealed up the hoses mentioned earlier. Before I sealed them up it would idle steady, but quit lumpy at 750rpm. I should mention I believe the AFM has been adjusted.
Also, it pulls very strongly and evenly through the full rev range. No hesitation at all

[Binkerment]

Last update. Adjusted the AFM and managed to get the idle to settle at aeou d 750. Still sounds lumpy but no erratic idle or hesitating when driving. I'll see how it starts tomorrow and take it from them. I've currently got it booked in for a smoke test and set up the AFM on a gas analyser.

[Binkerment]

Well, hopefully I've finally sorted this issue.
After checking and double checking the vaccum hoses today I decided to remove, test and clean the injectors.
During removal of the throttle body I noticed the gasket between the throttle body, hearing plate and manifold was damaged. Obviously someone has had it off before and didnt fit it properly.
Once all back together, car now idles much more smoothly. Still not 100% but almost.
The car is a non CAT model so is there any way to set up the AFM without a gas analyser?

[paultv]

The only AFM adjustment you should make if any is the idle mixture which sits under a blue or red plastic cover...it's a hex 5mm IIRC..but you need to hook up to a gas analyser.... ask your local mot station/garage for 5 minutes...as long as the engine is warm, set the CO to 1.0 at tickover using the hex adjuster, then never touch the thing again.

If someone has frigged with the internal spring position of the AFM you're kinda screwed. but you can usually tell if the cover had been removed and re sealed.

There's also a number stamped on the alloy next to the mixture adjustment hole, this the depth/ height of the hex adjuster to the top surface...example 17.5...use a micrometer to measure and adjust the screw thread accordingly, Mine was always too rich if I followed this method, I guess too much wear and tear since it came out of the factory, and the AFM may not be the cars original anyway.

Good luck

Paul

[Binkerment]

I was told never to mess with the idle screw so never have.
Someone else has messed woth the CO pot on the AFM so I'm trying to get it back to a factory setting. Is that what you mean when you say somethings is stamped regarding the depth of the screw?

[fixedwheelnut]

I was told never to mess with the idle screw so never have.
Someone else has messed woth the CO pot on the AFM so I'm trying to get it back to a factory setting. Is that what you mean when you say somethings is stamped regarding the depth of the screw?

The only way to set the AFM accurately is with an exhaust gas analyser hooked up to measure the exhaust output.

[paultv]

Yeah..setting to the stamped number is hugely unreliable... I set mine this way and got a CO of 3.5...on the 2.5 litre m20 it should be 0.8 to 1.2...so I ran it on a gas tester and set it to 1.0.

And no never fiddle with the butterfly end stop, it's not an idle afjuster at all, it's simply to stop the butterfly jamming in the inlet of the throttle body.

Paul

[Binkerment]

I know there's so many variables regarding the CO value. But if I measure the voltage at the grey black wire on the AFM it varies depending on CO pot adjustment. If I get the voltage off a known good M42 engine and set mines the same, would this set my CO level correctly? Obviosly a gas analyser would be better though