Newbie with an interesting question

[marty1979]

Hi all. I've been looking at this site for a while now with the intention to get an E30, I must say the forum is great. I've just bought a 1988 320i and am very very pleased with it, what a machine. I decided today to have a go at checking the valve clearances to try and solve an idle problem, but whilst under the bonnet I decided to remove the oil filler cap whilst the engine is running, and strangely it nearly stalled. I replaced the cap and it picked up again before returning to the lumpy idle. I'm pretty sure the idle problem is attributed to the fuel pump, any ideas on the other thing? If you say it's to do with the ICV I'll understand right away. Many thanks in advance. Pics of the car to follow.

[stuartgallafant]

sounds like its getting too much air and not enough fuel, and the fact that you have removed the cap has upset the air balance inside the engine

[marty1979]

Not enough fuel, thought as much. The fuel pump's far too noisy, so as I suspected that's the problem. Thanks for your quick reply.

[bimmaman]

I decided to remove the oil filler cap whilst the engine is running, and strangely it nearly stalled.

Isn't this quite normal? Well mine does it as well, anyway!!

[DRIFTBOY]

I think that is normal due to the large breather pipe on the rocker cover.

It feeds in air to the other side of the throttle butterfly than the airflow meter so the engine takes in un-metered air.

Hence a bad seal on the oil filler cap can cause a lumpy idle.

[Barnz]

I had this lumpy idle when I removed the oil cap on my 325, just presumed it was an air (pressure) supply problem and put the cap back on.... nice to see everything moving nicely inside though!!!

[320Touring]

my m20b20 does that, same as any other one i've owned.

dont worry

welcome dude

[marty1979]

Thanks for all your reassuring replies guys, hope to see some of you around in the future. If you're in the Bristol area and fancy a mini meet then give me a shout. Thanks again.