o2 censor
Like many engine and diagnostic parts of the 1990 Toyota Celica, the tachometer needs the assistance of a fuse to operate correctly. Check the fuse box for a blown fuse for this instrument.
Check the fuse!
You may want to check your catilick converter or your crankshaft positioning sensor.
Check: Autotrader.com NADA.com Edmunds.com KBB.com
It is probably your EGR valve causing the check engine light. I recently bought a used 1997 Toyota Celica and had this exact problem. The new valve cost approximately $85 and fixed the problem right away.
there is a reservoir on the passenger side of the engine bay, two levels are mark'd on it... hot level and cold level, depending on the engine temperature.
check the CV joints or the transmission is slipping
If fuses check out fine, then check the dashlights and taillights themselves, if those check out then most likely there is an electrical problem elsewhere
You might have to much oil in the engine. Check oil. Clean spark plugs. (remove and use sand paper to clean)
Same place you check it.
check the gas cap... usually if you "lost" yours and/or it isn't tight this could cause the check engine light to come on
I would first check your PCV valve, this was cracked on my 93' Celica GTS and caused that problem. It's very ease and cheep to fix. If this doesn't seem to be the cause of the problem I would check your air intake hose and vacuum lines.