I was a die hard thirdgen guy before I came to Buicks. I still love thirdgens and hope to go back to them (call me crazy)
85-89 cars are essentially the same with minor differences
My memory might be a little rusty, but as far as 305 cars go 85 tpi cars came with a better camshaft, generally good rear end gears. 86 went to the infamous peanut cam and IIRC hp dropped to 190. 86 LB9 (305 tpi) is probably the slowest tpi car ever produced. Typically 2.73 gears with the 7004r. 87 was the first year of the roller cam but it was still a peanut, last year for the 9th injector. HP increased slightly. Things stayed about the same till 89, 90 is when the SD TPI came out. Sometime in 90 305 cars started getting the good cam.
5 speed cars all got the good cam (FWIW I dont think there were any 5 speed TPI cars produced in 85 or 86). This is of course excluding all TBI engines which came with horrible cams and heads, and any carbed LG4 engines which If im not mistaken stopped coming off the line in 87.
T top center piece tends to rust. The biggest thing with Trans Ams (and to a lesser extent camaros) is that the air dam underneath the radiator core support MUST BE IN PLACE. Without this airdam the car will overheat almost immediately. These cars tend to run hot, and its very easy for them to overheat when any part of the system is sub par. I suggest either learning to program your own chip to get a lower turn on temperature or hooking up the fans to a lower temperature fan switch.
other problems include
Very slow power windows. They will make turbo buick windows seem fast.
Trunk hatch pulldown motors.. the dumbest "feature" ever added to a car. Every single one I've seen has gone bad. Either get yourself a non pulldown latch mechanism from an earlier car, or tack weld or bend the tracks in place so the mechanism doesn't move.
I never had a power antenna car but i hear they are miserable failures too.
The hood and hatch struts will probably be bad. These can be a little pricey. When I bought mine back in like 98, i remember the front struts were 11 bux a piece, and the rear struts were like 30 a piece. I can only imagine what they are now.
The popup headlights are another problem area. In the stock motor/gear setup there are these circular plastic pins that hold the center of the gear in place to the outer gear. These pins start to get smashed up till there is essentialy nothing holding the gears together. The headlights will start to only half pop up, or hesitate and youll hear the motors whirring but nothing happening. An easy fix is to get a wooden dowel and make new pins out of the wooden dowel. Works like a champ but is a little tedious to do. Out of several headlight assemblies and cars, i never had a bad motor. It was always these pins.
Aside from this I've seen a lot of problems in general. Code 32 for the EGR valve is quite common (if i remember the code correctly) it will only come on at random at cruising speed. Maf sensors tend to take a crap. Radiator cooling fan motors were frequently a problem. The fit and finish of the interior plastic parts is pretty terrible.
The good thing is that these cars are awesome platforms to go quick for cheap. I don't think you can touch one that has been prepared for road course duty with another car for the same amount of money. Autox is another story but they still are quite capable. They handle really well.
heres my old ride
305 .030 over, 214/224 cam, 416 305 h.o. heads i ported and had milled to 51 ccs 1.6 rockers, torker II single plane. Was TBI, converted to Edelbrock 600 cfm carb, converted from auto to t5 5 speed, 3.42 gears with a powertrax locker, headers, exhaust etc etc. Ran 13.6 with a 2.1 or .2 60 foot at 104-05 mph. Crazy huh? If you put that much work into a buick you are deep in the tens. Of course looking back on it I would have gone turbo on the thirdgen.
