1990 Sierra 2.0 GLS, when started the it usually doesnt idle correctly, it dips down below 500rpm then goes back up to over 1000rpm, it goes up and down for around 20 to 30 seconds then just dies out altogether but always starts no problem...........any ideas on what the problem could be anyone??

thanks in advance

 

NONE OF THE SIMILAR THREADS ARE SIMILAR TO MY PROBLEM IF YOU KNOW WHAT I MEAN


ANYONE ANY IDEA??? seems like a sensor or something

 

I assume this is a twinky engine ?
I would be looking at mixture related things, is it fine when hot ?, try cleaning the iscv.
tabetha

 

its 2.0l twincam engine, no when its hot it does the same thing.....

 

I'd be cleaning the valve, and looking for an air leak, on induction side.
tabetha