Let's solve the EGR position sensor code 16

[econo_turd]

I have an 89 carb L, CA car. Recently it underwent a complete engine overhaul and general rebuild. The car has something like 400k miles on it and i inherited it last year. I got it to pass CA smog with a rebuilt Aisan carb, and all the vacuum hoses and routing are new and good. The only remaining issue is the check engine light code 16 which comes on intermittently on the highway.

It occurs when the car is at constant speed and light load around 65-75 mph. If i mash the throttle or lift and decel, the light will go away, but it basically is always flickering on and off during freeway driving. It sounds like whatever is controlling the EGR valve or reading the sensor may have some issues causing the thing to dither around instead of be at the correct spot during constant throttle periods. It seems like a control issue to me. I had tried cleaning the EGR i had, and then even replaced with a NOS unit and had no change. Any thoughts? Perhaps it is an upstream component that controls vacuum to the EGR?

[econo_turd]

I'll point to these 4 components from the troubleshooting manual that all connect to the EGR valve.
EGR solenoid valve 1
EGR solenoid valve 2
EGR Modulator valve
Vacuum delay valve

The only problem is the guide doesn't really describe how these components SHOULD work. Based on my experience with control systems, I have a hunch about the "Modulator valve" purely based on its name. I think ill start with a visual inspection and see if I can make any sense of it with a hand vac pump.
IMG_5271.jpg

[WmWatt]

Also have '89 carb. Reach under valve and gently push up to check if rod moving freely. Valve opens to feed exhaust gas into intake to cool engine to reduce nitrogen in exhaust. At high speeds engine may be running warmer? Can only suggest removing valve, turning upside down to check rod not sticking or diaphragm torn. My check engine light came on once when that side jacked up in garage. When level back on ground light went off. Strange. Have cleaned EGR when smog test showed nitrogen getting high. Cleaning brought nitrogen down. No problem since.

[WmWatt]

PS Does "hoses good" include tight? I have knocked a vacuum hose lose and had light come on. Won't hurt to push hoses on tight just in case small leak. Good luck.

[econo_turd]

The EGR valve moves freely but I can definitely double check the hoses.

[econo_turd]

Also im not sure how this thread got duplicated.

[econo_turd]

This thread isn't dead, I just haven't had time to pull the modulator valve off and test it. We will get to the bottom of this.