Engine idles too high?

Hi hsv_mikej and welcome to 2carpros

1995 Chevy Silverado 1995 C1500 350 5-spd fast idle problem

Scan the computer for DTC's

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.

Hi 05chance, Welcome to 2carpros and TY for the donation

Try these test the coolant temperature sensor could be locked-up in the open loop mode and computer giving fuel when not needed, clean the mass airflow and EGR valve out-also check fuel pressure if its within specs-also check the fuel pressure regulator and for a clogged fuel return line.

Check for a blown gasket at base of tbi unit and drive steady over 40mph for over 2 minutes then see if it's still high.

Onthese just rplaceing iac is not all that is done you have to drive it for the iac to reset

Check for a vacuum leak as well. Any unmetered air will cause them to idle higher.

Clean out the idle air control valve/throttle plate and check acc. Cable if its kinked and test the throttle position sensor and manifold absolute pressure sensor

If the check engine light has come on, there should be a trouble code stored in the computer. I recommend taking it to a nationally recognized parts store and have them scan the computer. Most will do it for free, and it will direct us to the problem. Ask them to write down the codes for you so I can check it out and tell you what I think is the problem.

Joe

Check your base of tbi unit for a blown gasket you can spray choke cleaner at the base and normally the rpm will change if it leaks. It probably is as this is one of the problems that crop up due to age. You'll just need to replace the gasket. Also check for soft hoses going to pcv and map sensor on firewall. Have your brakes checked and mkae sure master cyclinder is full of fluid it may be a master cylinder going bad or brake wear or both.

Not necessarily, heat expands things, also when engine is cold it's not in closed loop so it's running a little rich, whenit warms the computer can't make teh difference up to richen the fuel pmix enough to overcome the vacuum leak.

Try cleaning iac then I fyou haven't already. But for it to reset you have to drive 40 mph for it to reset it self correctly. Only other thing I can think of is that iac is bad.