So I have a 1990 Toyota pickup 22re and my truck is throwing code 27 and 71. I know these codes are for the downstream o2 sensor and the egr. Has anyone else had these 2 codes pop up together? Will cleaning to egr help? Any tips would be appreciated, I'm freshly 18 and trying to learn to fix my truck, thankyou

 

The EGR system doesn't engage when the vehicle is idling, so that makes it pretty easy to test the EGR valve. You'll need a vacuum tester, and if you don't have one the chain parts store usually have one in their tool loaner program.
Start the engine and connect the vacuum hose on the tester directly to the EGR valve (do not connect to modulator valve). As you pump you should hear the engine running worse and worse, maybe even stall. This would mean the EGR valve is working. If the applied vacuum has no affect on the idling engine the valve could very well be clogged. They were prone to that. You just need to remove the valve and soak the passages with brake cleaner. then clean out. Pipe cleaners work well for cleaning out the passages. When you're done just check that the valve holds vacuum, then reinstall.

Exhaust carbon will clog the valve over time. While there are other components in the EGR system, the valve itself is the only one that comes in direct contact with exhaust gas.