Engine start but won t stay running

https://www.engine-codes.com/p1621.html

This site has several possibilities including low voltage to the electrical system causing various drivability problems.

If you just replaced the battery or it went dead, it will need to relearn idle. If you push on and hold the accelerator down does it stay running?

A 2000 Isuzu would have fuel injection not a carb, so no choke is used.
You would need to get the computer checked for trouble codes, I would suspect a huge vac leak is the cause of the fast idle.

the brake servo needs refitting and ensuring correct torque

chock has a plate that is supposed to float between open and closed. when you mash on the gas, it is supposed to be shut, and vise versa.

Hi Richard, I'm not an expert on Jags, just a little jealous I don't have one. Looks like a very nice vehicle. Have a close look, inspecting all hoses and vacuum pipes on the intake manifold side of the engine for any damage or loose fitting. The problem seems to be a leakage of air which is raising the idle speed. Regards John

Mostly your MAF MASS AIR FLOW SENSOR needs cleaning.
1st Disconnect the battery ground cable
then open the engine air cleaner.

• Disconnect the MAF sensor electrical connector.
• Release the air cleaner clamp.
• Separate the inlet side from the outlet side of the air cleaner.
• Remove the MAF assembly.
• Disconnect the MAF sensor electrical connector.
• Remove the nuts and separate the MAF sensor from the MAF sensor plate.

As shown


then follow the steps in the video.
HOW TO CLEAN A MASS AIR FLOW SENSOR

if that did not clear your engine chocking then make sure there is no Vacume leak.
hope that helps

The coolant temperature sensor located near thermostat housing can cause those symptoms. If price at autoparts store seems high, try dealer, sometimes they are cheaper.

Go to your local Auto Zone and ask them to read your diagnostic codes. They will scan your codes at no charge to you. Write the codes down and reply back to me and we can get started.
It could be something as simple as a plugged fuel filter.
Good luck, let me know.
Regards,

soundl like idle air control valve sensor
try a clean .............if no better replace