service engine soon light and hesitation

Hey ya'll, i have an 87 fiero gt manual with about 97k miles on it. My dad and i just finished replacing the intake manifold gasket after it over-heated a little over a week ago (whew). Before it didn't, but ever since we got it all back together, it seems to hesitate around 2500-2600 rpms in all gears and the tach gets all jumpy. We think its a vacuum leak but we haven't really found any bad hoses or connections. Any ideas or advice would be appreciated.
Also, this has happened pretty much since i've had it: the service engine soon light comes on whenever i'm on the freeway going 70+ mph for a few minutes and doesn't go away until i turn the car off and turn it on a few minutes later? I've tried replacing the o2 sensor and making sure the plug wires arent touching. Thanks ahead for anything ya'll come up with.
-Chris

take a windex bottle and fill it with water, with the engine running spray around all vac lines, if the engine rpms change sudenly you found your vac leak.
take plate off behind cigarette lighter, thats where the plug for the computer is, take a paper clip and make a u out of it. put one side in the a and the other in b terminal, now turn ignition to the on pos. do not start car yet.
the servise engine light will flash once, pause then flash twice. it should do this 3 times then it will flash any stored codes. write them down. after you get the codes come back and we can tell you what they mean.

man that is awesome. i had no idea you couild do a self diagnostic for the car. i thought the paper clip jumper thing was only for timing. anywho, i got a code 32 and that was it.

egr selonoid. was that the only code you got
? i forgot to mention it will go threw and flash the problem codes and then flash the 12 code when its done.
check the egr with a vacume pump. it should should close with just 2 inches of vacume
check your vacume hoses to make sure there are no cracks

yeah i made sure it went through the 12 sequence again. i checked the solenoid, one hose had a cracked, replaced that but it still does it. ill check the vac on the hoses tomorrow. sorry, trying to cram as much hours as possible at the job before school starts.

yea my 86 SE v-6 4spd does the exact same thing with the check engine light at highway speed, i will try the paperclip test tomorrow to see if it is the same code.

BTW is this something that can harm the engine, or simply an emissions thing??? In short, is it OK to drive the car with this?