I have an 88 Chevy pickup. It originally started as a low idle when turning sharp either directing (and sometimes dieing) and evolved into the idle fluctuating up and down when you are straight. I don't notice this when driving, only when idling or turning. I took it to a Chevy dealer, and they said that it was a cracked engine bracket that is causing excessive load on the engine. They also said if the bracket completely broke that the engine would fail to run at all. I am just curious why it would cause a problem when you're straight and not turning. If anyone could help me figure out the problem, that would be great. They maybe right, but I want to be sure because they want 500-700.00 to fix this engine bracket. Thanks.

If idle speed primarily drops when turning or, for instance, parallel parking, focus on the Power Steering Sensor, which is supposed to increase engine speed (ECU senses additional load).

Yes that is what's happening, but it also happens when I'm for instance just sitting straight as an arrow at a stop light the idle is up and down even then.