I have a 94 z71 5.7. It has recently started getting cold here in Nashville and with the cold my truck has been acting up. Here is what it does. Yesterday was the first really cold day we had and on the way home from work was the first time this happened. When the truck was cold and shifting gears in stop and go traffic it shifted really hard especially from first to second and then to third... Once I got moving it was not as bad. I also noticed that the check engine light came on with all this.... I stopped to get gas and subsequently checked my trans fluid and engine oil and levels were good... After I pumped gas and started the truck (after sitting for several minutes)... The check engine light was off and the shifting issue was no more.... (Fast forward to today).... I parked the truck in my garage overnight because of the cold and there were no problems on the way to work this morning.... On the way home however after it sat out in the cold all day it was the same story as yesterday's trip home... The truck has 230k miles on it but the trans has been rebuilt within the last couple years... I am stumped... Please help!!

 

I am pretty sure it is an electrical issue. The CEL is the best indicator you have right now, so get a scanner to see what codes its throwing. A faulty TPS(throttle position sensor) can make your truck do this, not suggesting it is, but just saying for example. So check codes and see what numbers the are and post up so we can help.

 

Will do! Thanks for the advice. Ill let you know what i find out.

 

Ok my truck is a 94' model and the parts houses all say they only go back to 96'. Is there a way around this issue without having to buy a computer to check the codes? I have heard there is a way to basically hotwire the pigtail to get it to blink the code number but i dont know how to do this exactly...

 

Try goin to Autozone first and have them scan it for free. See what codes they pull up. Your truck is ODBI computer system. 96 and up has ODBII thats why.

 

I went to AutoZone and they told me they could not scan it. That is why I wondered about "hot-wiring" it.

 

For GM domestic vehicles made before 1995, the diagnostic connector is located under the dash panel by the driver side. To get the check engine codes to flash in your dash panel, use a jumper wire or a paper clip and connect terminals A and B of the diagnostic connector. Turn your ignition key on with engine off and the codes should start to blink. All codes should start with code 12 which is one long flash followed by 2 short flashes. This code 12 means the diagnostic system is normal and will repeat itself continuously if there are no trouble codes. Otherwise, code 12 will flash 3 times before flashing the fault codes.

 

The code will also flash three times. So it'll flash code 12 three times, then your actual DTCs three times. When the computer is done flashing codes, it'll flash another code 12.

Let us know what the codes are when you get them. I leave a paper clip in my glove box for just such an occasion.

 

I am going to try this when I get home. Sorry for the stupid questions but how do I read the codes. I assume a long flash is a 1 and short ones add up to numbers...hence the long and two shorts equaling 12 ??

 

Ok guys, so I got the codes. They are 22 and 35. I checked around and everything I can find seems to suggest that these codes point to the IAC valve and the throttle position sensor. Can you guys verify before I buy the parts to replace? Also I was trying to figure out intuitively how those parts could cause the symptoms I was experiencing. Anyone have an explanation. I just like to understand what is going on. Thanks for all the help with this issue!!