I just replaced the intake and valve cover gaskets on my 1990 RS 305 TBI, and now I have a new problem. At start-up the idle is very rough, and it stays at like 500 rpm's or so while idling rough, then after 3-4 seconds it clears up like it corrects itself and immediatly after it straightens up, the SES light comes on. So it's like the idle is rough, then it does something to compensate, and then triggers the SES light. Any ideas? I have tried to find a vacuum leak with no luck, and can't find anything unhooked, all the emission/vacuum stuff is right where it needs to be. Could timing cause this? Guess I am just looking for suggestions, it's driving me nuts. Thanks for any help!

 

Did you check for any vacuum leaks near the intake?? Spray some air intake cleaner around the intake manifold area and see if that smooths out the idle.

Another issue could be the timing, did you mark the position of the distributor when you put the intake back in or shifted the firing order of the spark plug wires putting them back on??

If you have a scanner, attempt to read the Check Engine Light and see what code pops up.