For a couple years now I've been plagued with the 4L60E tranny in my '97 Suburban going into 3rd gear "limp home mode" after a few shifts when cold. The code says shift solenoids. So my mechanic replaced them and serviced the tranny (which had previously been rebuilt). Same problem. Long story short I was determined to find the guilty component that kept sending my Burb into 3rd gear. (No first, second or fourth.) Luckily the truck would reset and shift normally after it warmed up if I shut it off, waited 10 seconds and restarted it. So I just adapted to that regimen. But I kept searching since it seemed to be related to hot/cold engine. In the process of elimination, I replaced the t-stat, water temp sender, water temp sensor (for the fuel injection), the ignition switch twice, the throttle position switch, the knock sensor, the trans solenoid wiring harness, the air temp sensor, the air flow sensor, Engine Control Module (ouch!), cleaned the contacts on all the fuses, cleaned the throttle body .....I don't learn too quickly I guess. Spent a small fortune but I wouldn't give up on my beloved Burb! Anyway, after saving up more money I bought an Idle Air Control (IAC). Got a good brand not a Chinese counterfeit part! Two screws hold it on the throttle body next to the throttle position sensor. Anyway, its been three weeks and no PO785 code has shown up. It used to be a daily thing. Don't ask me why it worked. I can't explain it. Maybe because the OBD II diagnostic system was fairly new at the time and wasn't totally without bugs. This was a 1997, with a 5.7 and 4L60E tranny. Hope this info helps somebody! Good luck y'all !!

 

Good going, man!

 

Thanks for the feedback. It might help someone in the future.

 

Good job.You just to have to keep plugging away sometimes. I am sure somebody else will have this same problem someday.

 

Thanks for the update, most folks don't always get back with the fix.