I have a 93 4 cyl EFI Toyota pick up. Sometimes the damn thing just won't start. I sprayed some WD 40 into the intake and it attempts to fire. There is this strange clicking noise coming from the air cleaner/ mass air flow sensor when it won't start.

I first suspected the fuel pump but it isn't a constant problem
Then I changed the fuel filter and the problem was still there.

Any ideas?

First, find out if you have gas at the injectors and spark at the plugs.

Check the ECM and see if there are any codes.

About half of the ECU codes stored on the first & second generation EFI Toyotas don't show a constant blinking check engine light therefore you must pull the ECU codes to see if a fault is registered.

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/ts/obd-i/bl-dtcs-36.htm
http://autorepair.about.com/library/ts/obd-i/bl-dtcs-53.htm
http://autorepair.about.com/library/ts/obd-i/bl-dtcs-71.htm
http://autorepair.about.com/library/ts/obd-i/bl-dtcs-90.htm
http://www.off-road.com/toyota/tech/codes/index.html
http://lcengineering.com/TechNotes/TechNote12.htm
http://lcengineering.com/TechNotes/TechNote13.htm
http://www.geocities.com/MotorCity/Pit/9975/dataBySubject/Engine.html
http://www.mad-mechanic.com/toyota/toyotaobd.shtml#obtaincode
http://www.freewebs.com/th3duke/22RE-ECU.mht
http://www.troublecodes.net/Toyota
http://members.igateway.net/~pscott/enginecodes.html
http://www.autobook.co.kr/data_links/toyota_trouble_codes.htm
http://www.autoshop101.com/forms/h27.pdf
http://www.showmesome.info/hilux/info/manuals/1KZ-TE/Page0096.htm
http://www.efisakh.narod.ru/at_toyota.htm
http://www.usatransdoctor.com/foreigntoyota.htm

Pulling the ECU 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 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 them 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® ™
Repairs tv's,vcr's,home/car audio out of my home
E-mail:sidneybek@yahoo.com
Dartmouth,Nova Scotia
Canada
1985 Toyota 4-Runner,solid front straight axle,factory cruise control,sunroof,22R-E,W56,RN60LV-MSEK,rusted rear step/towing chrome bumper with 245 000 KM

http://www.iwaynet.net/~nesda/May02/May18.html
http://www.iwaynet.net/~nesda/SonyAudMod.html
http://www.newark.com/product-details/image/mcm/image/32-9495.jpg
http://www.iwaynet.net/~nesda/June03/June0315.html
http://www.iwaynet.net/~nesda/Apr03/Apr033.html