I just got a 90 fc GLX. Its great. I noticed that at night after a short drive the Idle kinda starts bogging out. It drops almost to the point of shut off then shoots back up then back down until I shut the lights off and then it stablises again. Ofcourse its only noticable while I am stopped. I thought it may be a bad bac. The ac dosent seem to affect the idle much. Also sometimes when I cold start it the rpm dose not go to 3000. Any insite on the funny idle?

 

Almost all idle problems are caused by:

-vacuum leaks
-TPS misadjustment
-sticky/clogged/unplugged BAC valve

In that order.

 

I thought it might be a vacuum leak. Ill have to take some time and check. I dont know where al the vacuum hoses are. Is tps Throttle position sensor?

 

Yes.

You will find the Factory Service Manual in the FAQ, which will answer most of your questions.