1889 Isuzu Trooper 4ez cycl 2600cc fast idles too high hot at low downshifting speed, sometimes surges and although it drops abruptly as the car stops moving, it is mostly too high at idle (1500rpm). Gun it and sometimes it goes down to 1000rpm, but motly not. Has new 02 sensor and just cleaned plugs, rotor and cap, timing is on, all vac hoses in good condition, spray cleaned the butterfly valved of the common chamber. When I press manually on the air intake throttle link at the common chamber (air intake) I can get it to go down to 1000 rpm. Can't adjust it below 1000 and should be able to. Any sensors or settings I need to check or adjust? Thanks. Paul
The Idle Air Control Valve, (IACV)could be gunked up after cleaning the intake and throttle body. The IACV, (which controls the idle as the engine load increases from; power steering, air conditioner, headlights, changes in engine load and speed, other accessories, etc. Is usually at least part of the problem you are describing. If you look in the throttle body you might see one or two ports. They might not be easy to see on your truck, however the IACV lets more or less air in tohrough these ports to change the idle. After time it gets gunked up and, I have done the same thing, using carb cleaner into the throttle body gets it gunked up even more. So, on the side of the intake near the throttle body but in the intake manifold the valve is generally bolted on, has an electrical connector and has coolant hoses running in and out of it. Remove the connector and unbolt the IACV, leave the coolant lines in place. Watch for a seal between the manifold and the IACV as you will need to re-use it unless it is in bad shape. Clean out the valve until the valve moves freely and is clean. Bolt it back on and reconnect it.
Also, there is a fuel injector cleaner called BG44K. You might have to go to service station or dealership to get it. It works so well that after a acn or two, the engine oil has to be changed from all the deposits that it has removed. Try that as well.
I hope this helps. Let me know if you have any questions.