Engine and trans acting funny after tire size change

[Bamboo]

Hey everyone, new to the forum. I have a 1994 ford ranger 4 liter auto trans. 4x4 It's just turned 100 k. By coincidence or not the truck started shifting funny after I put smaller tires on my truck. It came thru with 265/15 and I had a tire emergency and had to put on 235/15. The truck starts fine has high idle few seconds then comes down. I shift into gear and start to roll then the idle goes up to 1500 or so without my foot on gas pedal. And when I come to a stop it down shifts late. I have no codes and have preformed several diag checks and also replaced my elect. Components. Does Anyone have any clue? I love my truck but this I'd driving me crazy. Thanks

 

[swynx]

tryed putting the original size tire on it?

i know different size tires will mess with the shift points but shouldnt be that bad?

 

[Hitchner2009]

do you have the same size tires all around? and i cannot stress this enough, make sure you have THE SAME SIZE tires on any given axle. If you have 235's on the drivers front, you MUST have 235's on the passenger front. If you do not your going to DESTROY your differentials in a heartbeat. So make sure all your tires are the same size.

 

[Bamboo]

Thanks for replies. Yes all tires are the same size. Also I'm not able to buy another new set of the correct size tires, especially to experiment. I'm looking for used though. To combat the issue I have reduced the size of the hole in the IAC motor gasket and this works it's shifts fine now. But it causes other probs. that are less troublesome.