You can try some cleaner, can't hurt, made no diference to mine though. Any of the well known names should be ok wynns, millers etc. My injector failed at 68k, it will progressively get worse until the flat spot makes the whole car shake at low revs. If you've got the tools, changing it only takes a couple of hours, less if it's No1 injector as you don't need to take the inlet manifold off. Injector will set you back over £200, less from ebay if you can find any. You can get them reconditioned I think.