[Mk2] [Turbo] erratic idle when oil cap is removed ...?

[Amebb]

Has anyone come across this issue before... my mr2 has a 3sgte engine in it and when you remove the oil filler cap the engines idle becomes very eratic and then the engine stalls...

Is this normal or a possible fault to be expected ....?

Thanks

[Slarty]

The way I remember it (and I may be wrong!) is that on rev1/2 it'll make the idle eratic but on rev3+ it shouldn't affect it. I think it's to do with the AFM.

[MarkDon]

You would never run with the cap off, so why worry?

Its probs down to oil pressure being messed up.

[Amebb]

I agree with you MarkDon you would never run the car with the oil cap off.

This is the first time i have come across a situation like this and was wondering if its a sign of a big problem or, is it something that is normal on the 3sgte engine ...?

Technically, there should be NO oil presure issues as such.

I have had new piston rings fitted, new big end bearings, new oil seals, new valves and other things too.

i will have a look at the timming to see if its spot on...

thanks

[raptor95GTS]

i'm sure this happens on every car. Isn't there a breather than runs to the intake piping so taking the oil cap off would introduce a lot of air to the intake? Or I could be talking rollicks

[djpkins]

sounds spot on to me Allan.

[Amebb]

Allan, you are correct. There is a breather pipe that goes in to the air intake pipe.

I will check this out tomorrow just in case there is a blockage in the breather pipe......

Thanks

[raptor95GTS]

if your car runs fine with cap on then why worry. Not like you are going to be running about with the cap off

[simpson_eh]

mine ran fine with it off, then i cracked a piston ring/piston and it used to have excessive blow by


maybe worth a compression check just for peice of mind

[Steve Horrocks]

What revision engine is it? As said a few times now, if it's a rev 1/2 with an AFM then it'll stall due to extra air coming in.
If it's a rev3+ with MAP sensor, it should run fine (like Simpson_eh above)

[Baker]

As said, is normal and a Pcv issue with unmetered air. You can actually do this in a similar way to pass the not emissions test, pulling the Pcv hose near to the cam area will make it run lean and with breeze through the test, with little demise to the running.
Saying that, if there is excessive air coming out of the filler hole there could be issues.

[Amebb]

I dont think its a compression issue at all. I have had new piston rings installed and its working ok on that side.

However, i will check the engine tomorrow to see what else it could be...?

Thanks

[Steve Horrocks]

Again, what revision engine is it. If it's a rev 1 or 2 you don't need to find out what else it could be. Just stop taking the oil cap off when it's running.

[Amebb]

Steve the 3sgte is a rev2 engine.

[turbotrouble]

it relies on afm u are losing blow by in the equation hence it goes wrong. dont do it it will bu88er stuff up af mix etc