Cylinder problems

[Caisterwoods]

Hi I have a problem with my z3 it's the 6 cly 2 ltr 1999, Starts up fine, drives well, but after returning to idle, it drops a cylinder, turn it off for 5 mins and all is ok, I have changed the plugs, I took the coil pack leads out one by one listening for the engine note to change, which it did until I got to the cylinder nearest the dash, no change seems as if there is no spark, I changed the coil packs around assuming it was one of those, but did the same thing on same cylinder. It has been on a machine and showed up no faults.

Like I said it runs fine until you sit in traffic for more than a couple of mins.

Be great if anyone has suggestions. Thanks

[Lazzzydog]

swap the plugs around to see if the problem moves to another cylinder.

[Bench]

I had this on mine recently.

Changed crankshaft sensor and MAF. Solved problem in full. While it was serviced also replaced both lambdas as were giving false reads when live diagnostics were taken.

I had no CEL light on although diagnostics did show crankshaft fault.

[Caisterwoods]

Thanks for the ideas, got a computer on it, stating fuel trim error and dropping 2 cylinders, reset the computer by pressing a button in prog, all fine for 20 secs then same errors started up, so took another cover off the top of the engine, one beside plugs and fount a air hose with a great big split in it, needless to say it solved the problem.

[Mike Fishwick]

This shows what I have been preaching for ages - a computer diagnosis is not as good as intelligent and logical fault-finding. Some owners with idle problems have replaced the idle valve, then the spark plugs, and then the Lamda probes, then the airflow sensor, then the camshaft sensor - and then found that the intake bellows had a hole in it!

Most idle problems are caused by air leaks.