A week ago check engine lighted up on my '90 ES250. It was on for two days, then turned off by itself.
Code showed was 71 - EGR, right? (Sorry. I don't have a manual )

I tried to suck on the tube which goes into valve, it opens/closes just fine, the hoses which I can see from the top look good.

Idle RPM behaves strange:
Say I stop at traffic light, idle can settle at 1200, and go down to 700-800 in about 1-2 mins. Or it can go right down to 700-800. Is it related to EGR problems?

I get also quite a lousy mileage - 17-18 city MPG and 23 highway.

Tune-up 2K ago.

What should I look into? Thanks!

 

I'd look at some common culprits first, I'm still not 100% familiar with the ES as I'm just a prospective owner (looking at 97+ models) As far as the idle problem goes, in the different cars I've worked on this has been caused by: Bad ISC (Idle Speed Control motors) Poor BISS adjustment (Base Idle Set Screw) Poor Throttle Cable Adjustment, and as you've mention dirty/defective EGR Valves.

As for the fuel milage, it was just tuned up so I'd guess new plugs, air filter, oil filter etc were done. Ensure the plugs are gapped correctly and take a multimeter to your o2 sensor. It could be on it's way out, and that will KILL gas milage. Good Luck.

 

Thanks for your reply!

So let's assume EGR valve for now as it correlates with both MIL and bad idling.
How do I check EGR valve correctly? As I said, I just sucked on the hose which goes in there and plate inside moves up and down. Are there several of EGR valves?

What should I read off oxy sensor?

Car has 158K on it and I got no clue when it was replaced last time
Everything else (Filters, plugs/wires, fluids - BF to do yet ) I did 2K ago.