+1 also do this FIRST before any of that other stuff: if you don't check this the rest will be in vain:It could be your coolant sensor---
Other suggestions:--Check Ohm's:
-TPS, throttle position sensor
-ICS, idle control sensor
Battery / alternator / ignition coils
The very first thing I did just now was to unhook battery, remove battery tray (4 bolts, 10mm) and then remove the ground wire that goes from the negative battery cable to the fender well just under the battery tray. I ground the paint off of the area around the bolt with some coarse sandpaper, sanded the washer end of the negative battery cable that attaches to the fender, and the bolt threads that attach it all together, and then wiped it clean with acetone. Now apply dielectric grease to all the areas you sanded, and reassemble it all. This is vital to do on old / high mileage vehicles. Bad grounds can cause fires, blown fuses and relays and sensor / instrument failures.
This takes 30 mins and basic tools and no expertise.