i have a 1989 pick up 4x4 with a 2.6 and 5 speed. i am having problems with cold start idle as well as hot engine idle. it idles very rough and low at cold start. after it is warm it idles better but it is up and down like it is searching for proper idle speed. i have recently replaced the oxygen sensor and have just replaced the cold start sensor. i have checked the idle air solenoid on the fender according to alldata information and it shows as bad. i have talked to local isuzu dealer and they say replacing this solenoid will not fix the problem i am having. any ideas?

You might want to look for a dangling vacuum line or a hole in the air intake past the MAF sensor. Any fuel injected engine operates as a closed system with carefully metered air and fuel. Introducing excess air confuses the ECM. All the ECM can do is look at the air flow, look at the engine temp and adjust the gas injection rate. Air introduced past the MAF will give you poor combustion and a bad signal from the O2 sensor which will send the ECM hunting for the right mix. Any air leak would have the same effect so check the gasket on the intake manifold and the valve cover too.

In the factory shop manual it says to test the throttle postion sensor too and that might be bad if your idle air valve shows bad.