93 silhouette 3.8

Got a tune-up it it ran oh so sweet, plugs, wires, the whole bit. Then, a week after the tuneup, it began running rough for a couple of blocks. After that, oh so sweet. Getting 28 mpg at 65-70 mph. This went on for a week and now it runs so rough that the front end shakes like tire out of balance. My repair guy isolated it to the #4 cylinder. Pull off the plug wire, and the miss disappears. Lots of spark. What's strange is that it ought to run really rough with a wire unhooked.

No codes show.. Any suggestions???

Thanks...kenn

Check to see if you don't have a wire on the wrong cylinder. It's kind of a longshot, but if it's the right, wrong cylinder you could get crosstalk and ignite the fuel in an adjacent cyl or the intake manifold. Also check the wires, there is noting saying that you don't have a bad wire or plug out of the box.
Good luck
94

Well, That'sexactly what I suggested to the mechanic but he just couldn't believe a new wire could be faulty. It ran great for two weeks....Can it run that smooth if the wires are crossed?

I did put a bottle of injector cleaner in it and that seems to have cleared most of it but maybe it needs another bottle?

Thanks....kenn