I've been chasing a surging idle for a while on my 93 k1500. Checked all the vacuum lines, replaced EGR valve and solenoid (which did help with some hesitation but not the idle), cleaned throttle body, air filter, etc. My Haynes suggest fuel pressure next but it doesn't seem right. TPS or IAC seem more directly related.... thoughts? Usually between 400-500 rpm then randomly up to 800 and back down to 200-300 before resting at 400. (Never hits 1k at idle. I don't know where it's supposed to be.) But the surges are rough and jerky and only after it's warmed up.
Also, got an EGR code 32 AFTER replacing valve. Only shows after warmed up and at highway speeds for a few miles. Isn't that when IAC gets reset? Read that in another post.

 

Regarding the EGR, code 32 can set if the intake passages are partially or completely restricted. The restriction causes a lack of flow of EGR gases.

The ECM monitors the MAP signal to detect EGR flow. As the valve opens, intake vacuum lowers and the change is reflected in the MAP signal. Restricted flow = MAP signal beyond calculated or calibrated range.

Remove the EGR valve and use rigid mechanics wire to probe/clean the EGR passages. The most likely restriction will be located between the EGR valve and exhaust as this is where the most significant temp change takes place and carbon buildup occurs.

If it’s really bad, use a 1 foot length of small steel cable (3/16” or smaller) and fray one end, secure the other end in a drill, and then slowly “grind” through the passage to clean it. The cable will walk itself through the passage as the restriction is cleared - you need only to maintain light forward pressure on the cable.

Code 32 can also set if the MAP signal isn’t changing due to a faulty sensor or wiring issue.