engine surges before going into gear

[tugboat94]

my 1994 4.0L automatic will surge from 900 rpm to about 1500 then drop down and only then go into gear. what am I looking at. thank you for any help

also what is average mpg for this truck

 

[bikerboy]

You should check you IAC Valve. Pull it off and clean it with some carb cleaner. When was the last time you did plugs and wires on it? Hows the air filter look? How olds the fuel filter?

 

[tugboat94]

The IAC checked fine on a VOM. I cleaned it out with carb cleaner. I pulled all the plugs and found #2 cyl. plug was crusty and the #3 plug also but not as bad. I thought maybe the surging was a valve body problem. I ran the diagnostic test with a analog VOM and got codes 113, 121, 122, 172. I checked the TPS for voltage and also resistance and it seemed fine. I don't understand the 172 code. Which side is bank #1.

 

[jeffy56]

My 94 does something similar going into reverse, when cold.

Could the tranny valve body is getting real sticky. I'm told by my real sharp trans guy the rubbers get old, hard, and crack, then this can happen.

Also check vacumn lines to tranny.