i have a 84 gsl-se with a 88 13b in it. it's ran by the 84 ecu, has 84 front cover and dizzy, oil pan, oil cover, fuel rail and injectors, the injecotrs on the intake and pluged by RB's injecotrs plug setup, the acv is gone(along with the pump). it has the 84 BAC on it, and all 84 sensors. custom intake with a cone filter(air box it gone). i just resently finished the transplant. the car drives great but it idles bad. it'll idle down to 800 then jump to like 1200. it just keeps doin it. i talked with a friends of mine, he said that i need to put the egr back on the engine b/c 86- 88 engines had a problem with it and need it to idle properly.

 

The egr valve? I've never heard of that affecting idle. It sounds like you swapped everything from the 84 onto the s4 block, correct? Sounds like a TPS problem.

 

nawi sawped the TPS. it has all 84 sensors. i'm using the 88 intake and block pretty much.