Spark plugs. Now I changed spark plug tube seal, and spark plugs are basically dry. But code 0172 still comes up, idle still has trouble, while turning rate waves between 400-800.

 

today I found somewhere on passenger side leak either oil or transmission fluid. I checked one part of transmission fluid, which is shown by a stick, seems no leaking. Another part of transmission fluid is under the engine, somewhat hard to check.
I checked the engine dipstick, somewhat low, seems leaking. If it is true, then very probably oil pump. But I changed oil pump seal like 1 year ago.

 

Does the engine have a distributor with one ign coil and individual plug wires or two coils that each power two cylinders, or ? Could be a bad coil, plug wires, etc.

How was the A/F sensor located ahead of the first emissions converter?

The idle is too low. Should be approx 750 rpm. Does the idle pick up when the A/C compressor is running?

Make sure the EGR valve is closed when the engine is idling.

Check PCV valve system.

If an oil pump leak, it would show up as a steady drip/flow from underneath the timing belt bulge where the oil pump is when the engine is running. No flow when engine off.

The trans may have two sections for checking oil. The dipstick and the differential housing. The housing has two fill ports and plugs. One is under the differential housing where the axles install and the other on the firewall side to fill the housing. To check this fluid remove the fill port and the fluid should be at the same level as the bottom of the fill port hole. As recall the differential and trans use the same type of fluid which is stamped on the dipstick. Dexron III or whatever it is called today such as ATF. If you are going to change the differential fluid make sure the fill port plug is not frozen closed before for draining the housing..

Check dipstick trans oil with trans fluid hot, engine at idle after moving the gear selector between P and L and back.

 

My lousy job! Since I am not a professional and many times I take risk, I often made mistakes. Yesterday I thought I fixed my trouble of leaking because I found I didn't tighten up 2 screws for my water pump. But today I found it was still leaking, so I opened up again and found more lousy job. The oil pump gear nut loosen up with the seal coming almost off. That's why oil leaking.

 

At least you caught it in time! Had one oil pump seal leak that was losing 1 quart in 30 miles. Drip, drip, drip.

 

Since I had 2 days off, I pulled out intake manifold and cleaned it with water and detergent. Though I did that, idle problem still there. I never use A/C, Just now I tried. Yes, when A/C is on, turning rate get 1000 or slightly more, and steady. I checked PCV valve, no problem, I even used glue gasket seal for the contact there, no improvement.
I don't know how to "Make sure the EGR valve is closed when the engine is idling". Once I tried to stop EGR valve to intake manifold, and it is significant help, so I bought a new EGR valve. Yet the problem is still there. I changed EGR control solenoid last year, I bought a new EGR modulator and problem was still there, so I returned back. I may have 2 issue trigger idle problem at the same time. Now I've solved one: spark plug tube seal. Another, EGR system still there? I will test it tomorrow.

 

as said, while I am struggling fuel leak at fuel regulator.

 

But fuel still leaking.

 

Where is the fuel leaking. Can you take a photo?

As to the EGR system and testing, one can just turn it off as in the having the valve closed all the time. The valve is supposed to be closed at engine idle. The computer determines when to open the EGR vacuum valve based on coolant temp (warm engine), MPH, RPM, etc. The valve opening can then vary based on engine intake vacuum sent to the works EGR modulator to move the valve position.

 

Actually it is the first fuel injector leaking. In order to clean the intake manifold, I had to take it out. The fuel line is on the way. Just now I found the place and replaced 2 fuel injector o-rings. Now no fuel leaking.
I tried as youtube toyota guy said, opened the connection between EGR Valve and intake manifold, insert something in-between to stop waste smog get into intake manifold. Sure much better.