RPM jumps and jags when cold

[jbrodin]

Hi

There is a BMW 5-series 2008 up for sale. The seller is describing an issue with it:

“Car is in good shape and has been great runner. Currently has what I think a slight miss fire, though the dashboard does not show any faults, the rpm does jump a little up and down. Also when cold, put it in drive as you let go of brake the car jags forward, but as soon as it warms up it does not do it anymore.”

Is this most likely some easy fix like replacing a sensor or ignition coils or does it indicate something more serious/ expensive?

I have a Creator C310+. Would it likely show some code even if there isn’t anything on the dash?

Thanks,

 

[NZ00Z3]

Look for trouble codes and look at all of the fuel trims. It could be a vacuum leak that is bad enough to cause a idle problem when cold (open loop control) but closed loop control when the engine is hot can compensate for it. It might not be bad enough yet to pop the lean codes.

Any fuel trims > 8% indicate a possible vacuum leak.

 

[jbrodin]

Could it be a blown head gasket?