Engine over revs after head gasket replacement

I have a 1996 Toyota Hiace super custom with a turbo diesel engine. The head gasket was replaced but now it over revs. Any advice. Thanks

You have not given enough information for anyone to help you. Which turbo diesel engine? Under what conditions does the engine over rev? Did you replace the head gasket, or was it done by a shop? Was any other work done at the same time?

The first place I would look is your throttle position sensor, but without more specific info about your problem this is just a shot in the dark.

Good day,
Thanks for the information. My Hiace is a super custom serial number KZH1000023759. It is turbo with a 3000cc engine,1KZ-TE. A garage shop replaced the head gasket. The oil cooler cover had an internal hole upon inspection that was repaired and the cover replaced. The engine ran well but the engine now overrevs. The throttle position sensor is disconnected but it still revs up high. The reason for the head gasket replacement was overheating but did not experience any overrevving problems previously or any other problem with the injector pump. Thanks for the help

What do you mean that it 'over revs'? goes to the rev limiter with no throttle input? Idles too high? Only in Park, or while in gear?

you need to describe the problem in detail.

Good day, I went by the mechanic's shop. After a couple cranks the engine started and right away the engine speed shot up and the engine was in park. He had to shut it off because it was running very hard.
All of the electrical parts are disconnected and so is the throttle cable. Thanks for your help.

The spill valve on your fuel pump may have failed.  The engine should not start if it's unplugged.  You can test it with a multi meter.  I've heard that the spill valve may not test bad if it's stuck, so even if it tests ok, it might still be bad. The excerpt from the FSM says to replace the entire fuel pump, but this is not necessary. The spill valve itself can be replaced, and this can be done without removing the pump.

Thanks. I will proceed with your advice.

Good night, I have had a setback in trying to get my bus running. Latest problem ... a rat cut through the wiring harness that comes out of the battery compartment. Eighteen wires were severed. I can solder them back together. I have matched most of the wires as they are color coded. However, I have four brown wires that I cannot differentiate. They are the same size. Are these a common connection or do they have to be connected to the appropriate other brown wire. Thanks for your continued assistance.

Ouch! You've had some bad luck with your van!

Did you ever test and/or replace the spill valve?

Regarding your wiring problem there is a wiring diagram available for download from Hiacesoutheast here: https://drive.google.com/file/d/1eRUkCFjMLmHrfZ7lkwd0MfLwfvBiasIU/view

Unfortunately I don't think it has diagrams for vans with the 1KZ engine, but the other diesel vans (2L and 3L) should be very similar.

If you are lucky they are all grounds and you can connect them however you like. You could probably test them fairly easily with a continuity tester. Or open up the loom and trace them manually into the battery compartment. I believe there are a couple ground connections in that area.

If you have to resort to the electrical diagrams I suppose you could go through different systems looking for brown wires and then verify with a continuity tester. BR is the color code for brown. Not to be confused with B-R which indicates black with a red stripe. This would be a bit tedious and time consuming, but it is what it is. If you're not familiar with Toyota electrical diagrams do read the entire intro and how-to sections as it is not intuitive.