Nice to meet you, everyone. I am new here:)

Hello everyone, I am new here and it have been about a week since I bought 1988 Toyota Celica GT.
I do have at least two problems with the car. First one I believe is electrical problem, car was shaking at idles, lights were blinking everytime I pressed brake pedal or turned the fan, I thought it was alternator, went to mechanic, he did some tests and told that alternator needs replacement, so I bought Denso original new alternator and replaced old one, right after replacement everything seemed to be fine, but after like 15 minutes everything started to be the same. If alternator is brand new, can it be the battery?
Second problem is with acceleration, I went for a mountain trip, while going on highway I noticed that on uphill sections car wasn't accelerating even when I pushed gas pedal all the way it just kept speed at 70mph, fuel tank was almost empty although there wasn't any lights on the dashboard. ( don't know if celica have any )
I almost instantly that day replaced air filter, it is indeed was very dirty but no result.
I still have to change engine oil, oil filter, spark plugs, but I am not sure if those things are the root of the problem. Since that day I feel like car lost like 30-40hp.
My suggestion is that it has something to do either with injectors or fuel pump or fuel filter.
Oh and about general car condition: Well maintained by good old man, 186k miles, overall good condition.
Can you please help me with diagnose?
Thank you.
Here are some car photos:

http://cs540104.vk.me/c623424/v623424386/553b/gf4lvtDPak8.jpg
http://cs540104.vk.me/c623424/v623424386/4e6c/o8srk00Jwg4.jpg
http://cs540104.vk.me/c623424/v623424386/5527/nkbLJ_50hUU.jpg

 

Thank you
Here are some interior photos, although quality is really bad on first photo, I am sorry about that.
Photos:
http://cs540104.vk.me/c623424/v623424386/4e58/JJHPNNBKpPY.jpg
http://cs540104.vk.me/c623424/v623424386/4e80/0NuOjbAHyww.jpg

Today I have changed motor oil, oil filter, and almost all spark plugs, I got a little problem there, first three were easy to change, but I couldn't change 4th.
Basically I unscrewed plug and because I couldn't hook the plug with tool, I reattached the wire and tried to hook spark with it but failed.(did the same things with previous three and it was alright
then I tried to screw spark back to its place but it kept spinning, I started to panic because I thought that I stripped out the thread, but after like 5 minutes of panic I tried to screw plug once again and it worked.
I started the engine and revved to see if spark going to blow out and even ride at high rmps to check it but everything seems ok. So do you think I stripped out the spark thread and how I managed to screw spark plug again if so?
Engine was warm when I was changing plugs (was turned off for only like 30 mintues or so)

 

Hi. Never mind plugs, the thread is ok and I already changed the 4th.
After motor oil change, oil filter change and new spark plug engine seems to work better and I started to feel punch when I press gas pedal again, got throttle body cleaned today, now idles are much better, mechanic told me that I could be having problems with EGR, and some sensors, I don't remember which ones exactly, I do still have problem with idles but mechanic says it is not a alternator/battery/wires problems anymore. He did say that fuel injectors and overall fuel system needs cleaning, that's why I think I do really have problems with fuel pump as well. In my opinion engine is overall worn-out even though doesn't seem to have serious problems because was well maintained, it has 187k miles on it, and it already needs valve cover gasket, I don't know if I want to invest in 3s-fe, actually I am ok with idea of restoring this celica even if I exceed car's price, but I don't know about engine, in terms of performance I don't really like it especially old worn-out example of this engine which doesn't even make even stock power levels, I would like to do a 4A-GE 20 valve swap, but I do really want to maintain a stock look under the hood as well. Anyways all this not going to happen anytime soon so for now I will be drive everything as is, while fixing small problems.

 

Hello
When I was cleaning throttle body I examined that tube because I had to take it off, from what I have seen there was no holes or cracks, but I think I can have a look at it again, just to make sure, thnak you.
I think it is electric problem though, idle gets worse when I turn on headlights, blinkers or press brake pedal, I think some "-" wires attached to chassis are acting up.

 

Wow thank you, that's very useful info!
I will look into both grounds, I suspect they are causing problem.