Fred Harris

I have an 1988 Silverado 4x4 with what looks like a 350 engine. It has been sitting up for awhile. I just bought it. The engine idles way to high. I cannot find any vacuum leaks. I replaced the TPS Sensor, The CTS, The Thermostat, The CPV Valve. The gasket between the throttle body & intake manifold. I attempted to clean the Idle Air Control. Any ideas on how to get this thing to idle down. The timing is dead on. The code on an OBD 2 shows 22 & 24. The EGR Valve seems to be functioning as well.

GMcerttech

sounds like an issue with the computer. id have to do more research on those error codes but from what i saw in the 2 mins of looking it was pointing at a computer issue. double check all the vacuum lines. you may also have an issue with the fuel regulator.

Fred Harris

Thanks, one of those codes was a TPS issue, so I replaced it, the other is the VSS and I was told that one would not affect the idle.

GMcerttech

just cause the code is for a tps issue doesnt mean its actually the sensor you may need to track down the cause of the tps problem. make sure your getting proper voltage to the sensor. also check to make sure the throttle body is clean and clear of carbon build up. if there is too much build up it will hold the flap open too much and cause an issue like what your haven. also the vss code could be a sign of a transmission issue. VSS stands for both vehicle stability sensor and vehicle stability sensor as old as your vehicle is it should be speed sensor. if its reading incorrectly then your computer can be pushing more fuel then is needed. i would check it just to be sure. but more then likely its not the issue.

Camaro 69

Take off your air intake tube at the throttle body. In the bore of the TB, right in front of the throttle blade, look for some holes or a slot. Those are the idle air control air passages. With the engine running, put a finger over the opening(s). If that brings your idle down, your idle air control motor needs to be replaced. Clean doesn't mean it's working properly.

Fred Harris

I did replace the idle air control with a new one. Still have the problem.

Fred Harris

That is not the same as the idle air control that is an external device that screws in that has the plug on it is it? Your talking about actually in the throttle body bore itself?

Camaro 69

Yes, that is what I was talking about. The openings before the throttle blade is how air is bypassed through the idle air circuit. The IAC controls that air flow, so if it's faulty (not working or pintle not sealing when supposed to), you'll have a high idle.