I had the same problem in my 92 3.1L. It was a vacuum leak. Start with the vacuum reserve (black ball softball size under front left fender) from there follow the vacuum line looking for cracks or a break. Mine was broken at a 3 way intersection of the lines under the hood just past the battery. My cruise didn't work until I fixed it either. I have a post on here somewhere about that. I replaced the 3 way "T" that ran the cruise and the HVAC and that fixed it. Haynes was no help but there was a sticker by the fan shroud that had a basic diagram of the vacuum lines and that helped a little but it took several attempts to trace these lines and find the problem. I HATE vacuum line problems. Good luck.