Once again, GM eSI does not include this info for a 97 w / 5.7L, but if the engine has an IAC four wire stepper motor near the throttle valve, it can be controlled with hand-held tool. Most don't have one, but to make this easy, look and if found, unplug it. See if noise goes away. The shaft can strip and cause noise during seeking set point as per outside temp, coolant temp and the ECM demand. Using a scan tool like a TECH2 will have a "Special Feature" under the engine section, to control the IAC, increasing engine speed or lowering it. If noise goes away when unplugged, replace it, but clean the passage and throttle valve at the same time. I save old tooth brushes for this and many other tasks.
As for CSFI, the original stuff is poppet valves and over time, they will develop a sticky poppet valve due to carbon, gas evaporated crude ,etc. You can use a bottle of "Techron" by Chevron" in the tank when low to get higher concentration. The updated version is a complete updated assembly the has actual multec 3 injectors on the ends of the plastic tube with and little skill. With some parts, gaskets, o-rings and a weekend, you'll drop about $400+ into the project. A drop of 5 psi sounds ok, but obviously, no drop would be best. Remember, there is a check valve in the fuel pump supply, the fuel pressure regulator holds off return and injector is the only leak left unless external fitting.
Germans used poppet valve with constant injection system (CIS) but they sprayed all of the time, just at different volumes. As OBD-II set rules for mis-fire, poppet valve sticking became an issue as they can stick closed. California demanded a fix and engineers came up with second design. Trucks fall into a different category of emissions than cars, so at this same time, mis-fire counting was relaxed by the CARB in California as cars changed fuel pump design to hold fuel or draw it into a bucket that held the fuel pump. This later became standard on trucks as well. If cleaning injectors with can in tank do not help the 40 degrees start-up, fuel pressure ok and good 25kv spark, it's time to go deeper with scan tool or updated injector set. Note; 1 injector can be changed to electric, but it's best to do all at once. And use ACDelco. Don't forget to clean screen in the bottom of the distributor housing as it allows fresh air in and trapped ozone out. This is a commonly over-looked issue leading to premature spark failure, cap, rotor corrosion. This is why the rotor has a fan shaped bottom. Can be seen with mirror on a stick.
