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[terry paget]

X84GNB 2.5 petrol manual estate
I have changed RH exhaust manifold and gasket. This morning I put in battery and coolant and started up. Dismayed to hear exhaust noise around RH side of engine, and perplexed that on idle engine hunts 2000rpm down to 500, then up to 2000 again.

I wonder about the flexible pipe from manifold to EGR pump. Put this on last, might be leaking.

I bumped the idle control valve on reassembly, pushed it back into rubber on inlet manifold, seemed to be OK. I have wiggled it, no change.

Please advise.

[amba]

Seems to be pointing towards and air leak imho.

Worth double checking the short section of rubber pipe on the SAI that joins the 2 metal pipes as this is known to split and give symptoms you are describing.

[TheBoy]

I too would be looking for unmetered air, or a dirty ICV.

[chrisgixer]

Clean the icv with carb cleaner and light oil first. If it persists, pinch the hose to icv with your fingers. With a closed throttle and no air to icv it should stall. If it still runs the air getting in should be more audible and easier to spot.

If the egr valve itself is leaking it shows on top with sooty scorch marks. If suspect, it can be blanked off with a bit of tin can in place of the gasket to manifold iirc. Is the 24mm nut secure, is an obvious one.

[terry paget]

Thank you gentlemen for your excellent advice. You may read on a parallel thread that I have a serious coolant leak at the rear of the cylinder head, having been sold the wrong O ring to seal the transfer pipe. So I have to take it all apart again. It will enable me to examine the rubber hose connecting EGR pipes, the 24mm nut and flexible connection from exhaust manifold to inlet manifold, and the idle control valve.