I had a similar code a few weeks ago. P 1518, IMRC stuck open. It was stuck slightly open some of the time. The cable that actuates the secondaries was frayed inside the IMRC box so that it did not always fully return. I had to replace the box. If I recall correctly, it was about $130.00 list price. I had to drive it that way over a weekend waiting for the new part. There was a huge difference in engine performance once it was working properly again.
