EGR Code 32 Highway Mode

Since I bought my 1988 S15 Jimmy 2.8 18 months ago, I'll get a code 32 after 5-10 minutes of cruising at 80-100 kph.

The MIL won't light during town driving, just the highway driving.

The vacuum valve works, as does the solenoid.

I'm 99% sure I've cleaned out the head and manifold ports (a drop of oven cleaner and a piece of wire coat hanger works well). I tested the ports afterwards by blowing air through them (the exhaust valve was open).

Cooling system's clean. New temperature sender, O2. Electrical and vac connections sound.

Next step is to remove the inlet manifold and fully clean out the ports to eliminate that 1%.

Any information re enleanment in Highway Mode would be welcome.

What engine? Fuel injected or carb?
From the Haynes Manual Code 32
"Carbureted - Baro Circuit low, Barometric pressure sensor circuit low.
Fuel Injected - EGR, Vacuum switch shorted to ground on startup, switch not closed after the ECm has commanded the EGR for a specified period of time or the EGR solenoid circuit is open for a specified period of time. Replace the EGR Valve." Try cleaning it first, mine was almost plugged with carbon, a common problem.
I have a 94 S-15 Jimmy with a 4.3. The digital EGR can be a problem if carbon jams the pintel. Clean, work the pintel and add a little WD-40 to help free it up.
Good luck
94

Sounds like you need to replace the vacuum line going to the EGR.

I had an '87 vette with the same problem (32 code, highway speed light-up), and I did a whole top end, before seeing that a wire was chafed, and wouldn't carry good current to the EGR solenoid.