Is your check engine light on? If so, look to the right side of the brake master cylinder (towards the firewall) and there will be a small cap. Open the cap and there will be a diagram inside of the lid with a plug now exposed. Put a paper-clip to bridge terminal TE1 and E1... they are juxtaposed diagonally. Turn the key to the RUN position without starting it and watch for the check engine light. It will blink a number of times and then stop for a while and then blink again and then there will be an even longer pause followed by the same sequence aforementioned. This is the OBD-1 system for your check engine light. The first number of blinks is the tens place, ie: if it blinks twice and then pauses you have 2x. After the pause it will blink your tens place, ie: 5 blinks = x5. Thus you would have a code 25, which is a lean fuel-to-air mixture. This is the most common cause for a check engine light and rough idle on those Toyota motors. Check all of your vacuum lines, listening and feeling for air escaping or hissing. The breather line that goes from the valve cover is a common culprit and won't hiss, but will have oil around it if it's cracked. Most of the vacuum lines pop right off. If you can't find any cracked lines, clean the idle air control valve as previously mentioned. If you have another code then you can search for it by typing in "Toyota OBD-1 codes." If you don't have a check engine light then it could simply need a tune up.
