NEED HELP 1995 Sierra issues

My 1995 Sierra SLE is having some strange issues it has the 350 in it and it's 4x4 with 257,000 miles at first the check engine light would come on while driving come to a stop and the engine light would shut off and the truck would idle high tossed the scan tool on and there would be no codes now it's switched it's self and the check engine light comes on with a high idle at a stop throw the scan tool on and no codes again then it decides to start idling like it should and the check engine light would shut off and light up the check gauges light and show no oil pressure for about a second then oil pressure back to normal and the gauges light will shut off like nothing happened then on comes the engine light and then the temperature gauge starts dancing with a high idle then the engine light shuts off and everything is fine with a normal idle and still no codes and it's all intermittent both me and my friend are completely stumped we both went to college for mechanics and I've had the odb checked out and nothing wrong with it so what could be wrong?


Well-Known Member
I'd first start checking grounds and tracing wires. Gauges going wacky for a few seconds would more so be the connections rather than sensors or anything. I don't recall if the 95 is different than the later 98-00 but if the idle is going weird there is a servo that adjusts? It or maybe it's an air bleed I forget. Also use the scan tool to read Temps because ours read low or high but the scan tool always said right at 200. If it's not hot enough it'll kick up the idle and hunt it.

That Era of trucks is prone to electrical issues...


Gold Supporter
In addition to the weird electrical problems and strange Dashboard readouts... these other issues apply if your 1995 5.7L is using the "Old OBD 1" Engine Management System. And as for the Engine Idle problems, more than likely... you have already addressed most of what follows:

On A 22 year old truck… a whole range of things can cluster to cause problems... and so your Vacuum Hoses are going to be a little sketchy at their connection points and should be investigated when the engine is idling for being easily pulled off and obvious signs of age and cracking and a response to being manipulated that might pinpoint which . Next, your Throttle Body will probably have a buildup of Carbon and Dirt residue in the venturi chamber and around the Butterfly plate and might have tendency to “stick” open when stopped at a Red Light and allow air to bypass its normally closed position and cause the engine to idle higher… or “stick” closed and cause a jumpy start when you have to step harder on the gas pedal… making the truck lurch once the plate snaps free.

Again… when stopped at a Red Light and experiencing any “surging”… the (IAC) Inlet Air Control Valve mounted on the Throttle Body could also be clogged up with Carbon and be plugged up in the small air passage it controls to meter air into the engine when the gas pedal is not being pressed to maintain a proper amount of air by-passing the Throttle Body Butterfly Plate and keep the engine running and not allow it to stall. This is a non-serviceable component and an OEM replacement part is in order.

If The Throttle Body is equipped with a (TPS) Throttle Position Sensor… it might also need replacing, right along with the Throttle Body Gasket could also be sketchy enough to allow the unmanaged air to vacuum in below the controls mentioned above… and consequently… removing, cleaning and re-installing a thoroughly cleaned Throttle Body using only proper solvents that won’t damage any sensors. Disconnecting the Battery Negative (-) Cable just before a 30 minute servicing and cleaning of the Throttle Body will allow the vehicle to adjust to any replaced sensors. Using OEM TPS replacement units is recommended here… and New Gaskets as well.

One last problem that is often not obvious, but has been observed over time are Leaking Upper and Lower Intake Manifold Gaskets that allow Coolant Passages to weep Coolant around the perimeter of the engine. Unless its obviously present, this should be the last issue to investigate as these problems would also allow unregulated air to enter the Fuel-Air stream and cause the engine to idle quite high as more fuel is being added to compensate for the excess O2… especially when the engine is Cold… and this issue will not throw engine codes.

Here is a link to CRC’s site on the proper cleaner and techniques to follow: