87 idle problem

[Rescuedad77]

I just swapped my 87 GMC jimmy tbi 350 with an 81 350 block and cannot seem to get the timing right, I have brought it to three different mechanics around town who cannot seem to figure it out. One did tell me that the cam in the 81 block will not work in the 87 tbi setup because of the computer needs to be reprogramed. I called jegs up and they told me the computer cannot be programmed for that cam does anyone have ideas. Thanks!

 

[Cricket]

You'll have to either get the correct TBI camshaft or have a custom computer chip made to work with your non-TBI camshaft.

 

[btolenti]

I swapped a TBI unit on my 86 with the stock cam, and it ran just fine. I timed it to 4 degrees BTDC. My 86 spec (stock) was 6 degrees, and TBI is supposed to be set to 0 degrees. But mine seemed to work best at 4 degrees. Are you unplugging the brown wire before you try and set timing?

 

[Rescuedad77]

Yes, the weird part of it is at idle it runs like crap anything over ten miles per hour it purs like a kitten.

 

[BadBob]

You didn't set initial timing with the distributor plugged into the computer did you? I seem to remember having to unplug it to set it to 0* without the computer retarding the crap out of it.

 

[btolenti]

are you sure it's not an EGR problem (stuck open?)? Is the computer throwing any codes?

 

[Rescuedad77]

Chiltons told me to just unplug the brown and black wire.

 

[Rescuedad77]

the computer isn't throwing any codes at all.

 

[btolenti]

Sounds like it could be a vacuum leak or an EGR problem. Have you checked all the vacuum lines for cracks, etc.? Try unplugging the vacuum line to the EGR and plugging it with a screw and see if the idle gets better. The chilton's book should have a test for the EGR valve itself too.