Pull the ECU codes and measure voltages/resistances at ECU (EFI computer) and compare with FSM (factory service manual):
Free 1990 Toyota 4-Runner Factory Service Manual:
http://rapidshare.com/files/34006966...0.1995.SIL.rar
To pull the ECU codes:
All 1980-1995 and including 1995 EFI equipped vehicle allow you to find engine and related faults by pulling the ECU (computer) codes without the need for a handheld OBDII diagnosis scanner, the sites listed below have the fault codes needed to pull the codes and the instructions on how to do it:
http://autorepair.about.com/library/...bl-dtcs-36.htm
http://autorepair.about.com/library/...bl-dtcs-53.htm
http://autorepair.about.com/library/...bl-dtcs-71.htm
http://autorepair.about.com/library/...bl-dtcs-90.htm
http://www.autozone.com/az/cds/en_us...rInfoPages.htm
http://www.off-road.com/toyota/tech/codes/index.html
http://www.4crawler.com/4x4/CheapTri...CheckConnector
http://www.4crawler.com/4x4/CheapTri...osticcodes.gif
http://lcengineering.com/TechNotes/TechNote12.htm
http://lcengineering.com/TechNotes/TechNote13.htm
http://www.geocities.com/MotorCity/P...ct/Engine.html
http://www.mad-mechanic.com/toyota/t...tml#obtaincode
http://www.freewebs.com/th3duke/22RE-ECU.mht
http://www.troublecodes.net/Toyota
http://www.autoshop101.com/forms/h27.pdf
http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx
http://forum.ih8mud.com/79-95-toyota...ror-codes.html
http://www.showmesome.info/hilux/inf...E/Page0096.htm
http://www.efisakh.narod.ru/at_toyota.htm (auto tranny codes)
http://www.usatransdoctor.com/foreigntoyota.htm
http://www.obd-codes.com/forums/viewforum.php?f=3
Pulling the ECU (EFI computer) codes is the first thing I do to diagnosis a problem thereafter I reset the ECU to see if the same problems show up and if so I then take voltage measurements at each ECU wire both with the engine running and not and compare with the factory service manual, I also close the ignition switch after a cold engine and also after a warm engine and compare the resistance values with the factory service manual.
This technique will completely isolate your problem without having to do trial and error and it is the technique I use when repairing tv's, vcr's, home/car audio.
Sidney