strange running

Adam · Post by **Adam** » Mon 03 Sep, 2007 18:24

Driving home from work today my z3 did something rather unusual.

Driving along about 40mph, I dip the clutch to change gear and the engine cut out. I coasted up to the traffic lights and restarted no problem. But then the idle was erratic. fluctuating from approx 450-800rpm. once i put my foot on the throttle and drove off the car was fine. There was a quarter of a tank of fuel in the car. I drove up to the next junction and the idle was fine. then when i came to a stop at the local retail park and it went to idle again...it fluctuated. Gave it a rev...it was ok.

I normally use Shell v power or their normal unleaded.....but after a track day on friday I filled up at the garage outside castle coombe......I wonder if this has caused anything....maybe some dodgy fuel. Yet the car was fine on saturday & sunday ???

I filled the car with shell unleaded and drove home......as i pulled out of the petrol station it was fluctuating...then i gave it a blast up the road and home it seemed fine.

having just gone out to it now and let it run...there seems to still be a little bit of fluctuating when idle.

any ideas

mich · Post by **mich** » Mon 03 Sep, 2007 19:01

Adam, if a refill with fresh gas does not do the trick it could be the inlet camshaft sensor starting to play up, not a pocket breaking job, one thing this usually does is that the engine cuts out when pulling away from rest.
best of luck

Tourniquet · Post by **Tourniquet** » Mon 03 Sep, 2007 19:04

Had a similar problem a fair while ago. problem got steadily worse over a few weeks. took it to a specialist and had it diagnosed as a fouled/faulty sensor in the engine (Camshaft position sensor if i recall). for your sake, i hope it is nothing more than a little bad fuel.

SpunkyM · Post by **SpunkyM** » Mon 03 Sep, 2007 19:07

Check around the intake for any split pipes or air leaks. Sounds to me like some air is getting in the other side of the AFM and not getting measured properly. The split might not be very apparent so you need to check all hoses and connections carefully. If not that then the good old fashioned cam sensor might be a suspect.

Adam · Post by **Adam** » Mon 03 Sep, 2007 19:09

SpunkyM wrote:Check around the intake for any split pipes or air leaks. Sounds to me like some air is getting in the other side of the AFM and not getting measured properly. The split might not be very apparent so you need to check all hoses and connections carefully. If not that then the good old fashioned cam sensor might be a suspect.

that could be a possibility as i can hear the car hissing a bit around the inlet area. pulling or blowing air.

Z-ORRO · Post by **Z-ORRO** » Mon 03 Sep, 2007 20:32

My Z3 always idles at around 800 RPM, is there something wrong with it?

AndyBass · Post by **AndyBass** » Mon 03 Sep, 2007 23:55

2.8's had a tendency to split the plastic inlet manifold at the back, right where it's difficult to see. Apart from that I'd suspect a cam sensor. They work ok sometimes then give the symptoms you describe.

Zorro, 800rpm seems high for a normal warm idle, ok when cold but too high normally.

Z-ORRO · Post by **Z-ORRO** » Tue 04 Sep, 2007 22:44

Oh, i thought that 800 rpm was too low!!

I think that it's like that when it's cold/not run for long, and it seems to be a bit above 500 rpm after a while. It doesn't sputter or anything, seems to run very smoothly.

mich · Post by **mich** » Wed 05 Sep, 2007 00:38

When my sensor packed up I was idling @ 800-900 rpm. when new sensor was fitted it dropped to 600rpm and as smooth as.

///M_aniac · Post by **///M_aniac** » Wed 05 Sep, 2007 09:54

Z-ORRO wrote:My Z3 always idles at around 800 RPM, is there something wrong with it?

Not at all. Will drop a little more when she's warmed up.

mich · Post by **mich** » Wed 05 Sep, 2007 21:05

Idle speed is always quoted at running temperature, unless setting the choke as on old classics