Rough idling

[Chris Baker]

I have an 04 4.6 Disco II. I have changed everything thing but getting miss fire codes.. Will leaking O-rings on fuel injectors really effect the running of this engine?
At a cold start, it will idle high.... or go up and down and to the point it may try to stall. After a minute is seems to smoothen out. Once it warms up, it seems to run OK but at a stop or at park it has a tendency to want to idle from 700 RPMs to 1100 RPMs give or take. Bank 1 and 2 say they are running lean... I have replace the top intake manifold gasket twice and torqued at specs. . But if I spray carburetor cleaner in that area where the gasket and injectors are located, I do have a change in idle.
Mind you I had to put another engine in this Rover... So not sure how long this engine sat till I put it in the vehicle.
So I am asking, can leaking o-rings around fuel injectors cause this... I do have miss fires in multiple cylinders. I have new, plugs, wires, core packs.. So know the fire is not the issue.

 

[Swedjen2]

yes

 

[LRDONE]

Sounds like a vacuum leak to me? Especially if you're getting system lean codes.

 

[salvvia]

I have an 04 4.6 Disco II. I have changed everything thing but getting miss fire codes.. Will leaking O-rings on fuel injectors really effect the running of this engine?
At a cold start, it will idle high.... or go up and down and to the point it may try to stall. After a minute is seems to smoothen out. Once it warms up, it seems to run OK but at a stop or at park it has a tendency to want to idle from 700 RPMs to 1100 RPMs give or take. Bank 1 and 2 say they are running lean... I have replace the top intake manifold gasket twice and torqued at specs. . But if I spray carburetor cleaner in that area where the gasket and injectors are located, I do have a change in idle.
Mind you I had to put another engine in this Rover... So not sure how long this engine sat till I put it in the vehicle.
So I am asking, can leaking o-rings around fuel injectors cause this... I do have miss fires in multiple cylinders. I have new, plugs, wires, core packs.. So know the fire is not the issue.

Absolutely
Get a smoke test done thats how i found mine
Oring job is not as bad as it seems
TAKE YOUR TIME

 

[simondewing]

Much more likely the stupid rubber seal under the back edge of the lower manifold / valley gasket.

They go hard and crack creating a non obvious vacuum leak.

As you have already pulled the upper manifold you are 90% of the way there.
Just unbolt the lower manifold too and replace the gasket and the front and rear seals



Its held down by a metal retainer front and back as above.

Gasket forms the top of the push rod chamber which vents via the crankcase and breathers.
If its not sealed you will have a vacuum leak

 

[Chris Baker]

Much more likely the stupid rubber seal under the back edge of the lower manifold / valley gasket.

They go hard and crack creating a non obvious vacuum leak.

As you have already pulled the upper manifold you are 90% of the way there.
Just unbolt the lower manifold too and replace the gasket and the front and rear seals

View attachment 61460

Its held down by a metal retainer front and back as above.

Gasket forms the top of the push rod chamber which vents via the crankcase and breathers.
If its not sealed you will have a vacuum leak

Those gaskets have all been replaced.

 

[JUKE179r]

I remember an internally dirty IAC valve causes high idle.
A tooth brush and throttle body cleaner spray will help sort that out.

 

[discostew]

It sounds like a vacuum leak to me. Ckeck that that bracket that holds the throttle cables to the front of the plenum are letting the throttle return to the idle set screw. What cylinders are storing faults for misfires?