When I took the manifold off i noticed how charred it was @ turbo end. Pulled it straight to measure for a replacement, it was dust. Fell to bits. I replaced it with another earth strap. Used a copper lug and is fine with the heat. Put a multi from heat shield to chassis point and check resistance to see if it needs replacing.
If I understand correctly the earth strap is to prevent electrolysis, I doubt it would help your idle.