Rough Idling Evens Out When I Lift Oil Filler Cap..why?

[mac73 0 1 Cars]

My 205 1.6 will need 4 or 5 cranks before deciding to start then will sit on 1000rpm for a few minutes before starting to hunt to the point of dying.When the oil filler cap is lifted up while in hunt mode it instantly stops and evens out! I was under the impression this is supposed to make the running worse so at a loss as i have had the engine bay steam cleaned, pipes cleaned out and replaced all ignition parts other than ecu, afm and sad to find out cause for said hunting oh and stalling when coming to lights or junctions.

When i bought it 8 months ago it ran great and all i wanted to do was keep it that way but getting the timing belt and filters changed started strop of the decade! oh hum. Cheers for looking guys.

 

 

[welshpug 1,661]

its a sealed breather system as such, so when you pull the oil cap off you introduce unmetered air into the intake system.

[mac73 0 1 Cars]

So that would imply it's is being starved of the air it does need then when top back on yes? The breather pipes are clear although there was some gunk in them.

[Anthony 1,003]

Hunting is usually a symptom of too-rich a mixture, so that would tally with removing the filler cap and the extra unmetered air leaning out the mixture and improving the idle.

 

Try turning the mixture screw on the AFM anti-clockwise two or three turns and see if that improves things somewhat.

[mac73 0 1 Cars]

Thank you!! will try that and see what happens.

[mac73 0 1 Cars]

Hey guys i looked through the emissions results as had mot August (when not idling/hunting as bad as now) and

co = 2.41 and hc =273 ppm . Am i correct in assuming 2 or just under is better for our 205's ?

[welshpug 1,661]

around 1.5 is best.

[Anthony 1,003]

... or less. I typically aim for 1% or so.

 

Assuming its now richer than it was that would explain the issue - they simply don't behave nicely towards the upper limits for an MOT pass, made worse if the rest of the setup also isn't right.

[mac73 0 1 Cars]

Your not wrong there Anthony! The more she gets "set up " properly the unhappier she's getting although a pipe with a crack

was replaced not long after the test so the mixture would have been set with this leak in place so that will be wrong now

hence the hunting being worse! Does that make sense? My wonderfull bro will hopefully help me get it right now i have her

safely ensconced in the garage! If the tweak doesn't make a difference then it probably will be the dreaded AFM to replace hmm.

I do own a haynes owners workshop manual though so will do some delving re the set up..

Cheers guys

Edited December 11, 2015 by mac73

[mac73 0 1 Cars]

I would like to thank Welshpug and Anthony for their help with my dilemma! I"ve taken so long in replying as i left her in the garage over the winter but got her leaned out to just below 1.5 and the difference is unbelievable! No hunting or stalling at traffic lights or junctions and back to being well behaved.

Its annoying having spent lots of money changing this and that when the solution was so simple and took mere minutes to do!