I have a friend that has a 1987 Toyota 2WD, 5 speed manual pick up, with a carburetor. She is a single mother with little money to invest in getting this truck to pass emissions inspection, so I need any and help trying to determine what is wrong with little cost as possible.

When you rev up the engine in neutral the RPM goes up and down, so much that they can not do a emissions test since it will not run at a steady RPM to do the test.

I am almost certain it is somewhere in the carburetor system (I know how much this involves and could involve ), I just need to know where and what to check/look for.

 

Start simple: check air cleaner, spark plugs and wires, leaks in vacuum hoses, and all other typical tune-up items before going deeper.

 

On the EFI truck, those symptoms can be caused by having air in the cooling system. Try burping the cooling system by raising the front end as high as you can get it and let it cycle the Thermostat 3 or 4 times with the radiator cap off. I am 6 foot tall and the radiator cap is at my shoulders level when I do it so it is fairly high. Not sure if that will effect a carrbed truck but could only help it getting the air out. Maybe someone else that knows carbs better then I do can help.

I dont know if the Weber Carb will pass emissions in Utah but that is a far better way to go over the Aisin carb.

 

I know the efi engines do this if the computer senses the brake lights are on. Possibly you have a stuck brake light switch? I don't know if the carb engines can cut fuel or spark to make this happen but this was my problem with my 22re. Took me months to figure it out.