Hi Guys!

I did a search for "revs on its own" and "revs by itself" first but couldn't find a post with this issue. The quick backstory is this... I had my engine light come on a few weeks ago and along with that came the shuttering, sputtering, and hopping up and down when idling. From what I read in the posts, is that it's best to replace ALL the ignition modules (mine had the yellow stickers on the tops). So over the weekend, I replaced allthe ignition modules along with putting in brand new NGK Iridium IX plugs in my 2002 S-Type 4.0L V8.

The good news is that the car now runs GREAT and doesn't shutter at all (which was quite embarassing when I had passengers in the car). But the bad news is that after three "cycles" of cold starts, the engine light is still on and a new problem has surfaced. I now notice that if I'm coasting down from, let's say 40-55MPH, and get below that speed with my foot off the gas, the engine will rev all by itself between 1,000-2,000 RPM for about five or six times. It literally revs on its own up to around 2,000 RPM for a second then comes back down to around 1,000 RPM for a second and then back up to 2,000 RPM and so on.

Haven't a clue as to what this might be, but I'm guessing that perhaps that's why the engine light is still on?

 

I figured it might have something to do with the throttle position sensor, but it'd probably be better just to replace the whole thing, huh?

Isn't a new TB though around $1500? Do you recommend a place I could get a used one?