Few questions(new car to me)

Hi, im new to the board- I will soon be owning a 1990 GSX, (AWD not turbo) 5 spd this car will be my daily driver/ fun (prolly rally it in stock class) car. I have a few questions, #1 -- The a/c works, but when a/c is on idle drops down a little, most cars have some sort of selenoid, OR, tell the ecu to raise the idle so the motor does not bog, this must not be functioning correctly because the idle just drops, and car shakes a little(not bad but not something i'd like to keep that way) #2 -- The car has yokohoma tires on it, the owner said that they dont drive it much, and the tires are 2 years old, they have lots of tread so im assuming that they really didnt drive it much.. now what im wondering is, when i bring it up to about 70 there is a slight shake in the wheel, it really is not bad compared to times i have felt this in other cars, what im thinking it is, is probably the tires need rebalanced from not being used for so long, What do you guys think? anything else that may be doing this?. it seemed to do it wether under excell or not, and did not get worse with braking. #3 -- How well do these motors really last, from some people i hear they go forever, and others say the rings start leakin oil thru at 150-200k miles, the one im buying has 120k miles and does not seem to burn any oil whatsoever. Let me know you'r thoughts on the longevity of this motor-? , also- so far i have read that possibly the idle control selenoid may be the reasoning for the ecu's caps to go bad in the first place, so , i plan on taking that off and giving it a nice cleaning, is there anything else that i should mantain that may possibly go out(something that a lot of people have go out on these cars?) Let me know any thoughts you have- thanks for having this great site- i have already learned a good bit just by reading posts. Nick

the caps in the ecu are a separate problem, which you should take care of immediatly. put it off, and you will spend 1100 for a new ecu, or spend 300-350 on a rebuilt one, and probably have to send it back a couple of times because the rebuilder sucks. if the isc craps out, it can take out a couple of drivers in the ecu. the first thing you should do AFTER you get the caps in the ecu changed, is to reset base idle and base timing. also, the isc sits on the bottom of the throttle body, if you remove it, and be careful because there is an o ring that seals it, and if you lose this o ring, you will NEVER have a good idle-plug in the isc to the harness, and have someone turn the ign on, but do not start. you should see and hear the isc cycle in and out, and then stop. if it just sits there and vibrates, it is no good. in some cases, coolant will leak from the fiav chamber and short out the isc, which will then take out the ecu. btw, the transfer case on these cars is a problem area, check and see if it is full of fluid, and usually they all leak at the output seal, but it is not the seal, rather the yoke of the driveshaft. if the fluid is leaked out, the xfer case will lock up all 4 wheels.

The guy told me that some transfer case recall has been done, kno anything about this? I would imagine they replaced the seals while in there dont you think?