i have a 1991 rs that was a tbi with a 5 speed i transplanted a tpi from a 1989 iroc, i kept the 5 speed in the car switched the harness from the 89 into the 1991 rs the 89 iroc was a automatic, the problem i am having is the car stalls when i decelerate i have read some posts that say its because the spedo is not working i need some help getting my speedo working i swapped out the clusters but the speedo still doesnt work im not sure if its because the 91 had a vss buffer and the 89 didnt and there is some breakdown because i didnt use the auto trans and kept the 5 speed and the sensor from the 91 wont comunicate with the computer in the 89 harness i could really use some help thanks in advance for any help you can give

 

you could try changing the computer to the 89 one maybe that would fix the problem.

 

By what's bolded, I take it you swapped the entire harness and computer from the 89 into the 91?
When you swapped gauge clusters, did you happen to notice that the 91 speedo is electric and the 89 is cable driven? I'm not surprised either that didn't work.
Basically, you need to set the 91 up electrically like it was the 89. The 89 computer (what you have to use) didn't drive a VSS speedo, so you're going to need to convert the trans over to cable driven and use the 89 cluster for the speedo to work. The no VSS signal/speedo not working would be an issue with the 91 computer, the 89 computer isn't looking for that signal.
Your issue may be with a sensor that the 91 computer controlled, and the 89 isn't. Does the engine run fine, except for the stalling? After it stalls, does the engine start right back up? If it doesn't, it may be easier to diagnose by checking if you still have fuel (shoots out when you push in the shrader valve on the fuel rail), or if you still have spark.

 

the 89 had an identical gage cluster as my 91 except the 91 only went to 110mph the one in the iroc went to 145 there was no cable maybe somthing had been switched before i got the car and the engine runs great untill i decelerate i may be on the wrong track

 

I don't know if its a trans issue or not, clearing this up might help though. What CPU items did you swap exactly? Keep in mind that this is a completely different fuel management system and you will have needed to swap everything over from the 89. In essence you are removing anything that the 91 had and moving everything from the 89 over...basically making the 91 think its the 89. Are you having any issues at all aside from deceleration? I'm thinking its a fuel delivery issue.....not sure though.

 

i switched the entire harness from the 89 to the 91 including the cpu, the trans plug from the 89 which was an auto trans plugged right up to the 91 5speed the car runs great other than the stalling issue and every thing else except the speedo works i have read some posts that say without the speedo working the computer doesnt know what to doo when you let off the gas and it will stall how do i check and see if my trans is sending a signal

 

I used to have a 91, so I'm not just pulling stuff out of the air....
The 1990-92 gauge cluster has 4 small gauges (temp, oil, battery, gas gauge) between the speedo and tach, and the speedo is electric.
The 1989 and older cluster has 3 small gauges (temp, oil, battery) not 4, the gas gauge is in the tach, and the speedo is cable driven.
What are yours?

 

i would like to thank every one for there help i found the problem there was a broken spot on the wires from the speed sensor it had been pinched some where along the way during removal or reinstallation