Hello guys greetings form Mexico.

This is my first post about an issue I have with something related to the fuel mixture.
As a context I own a 1990 toyota pickup deluxe 4wd w/ 22re. This truck had been with the family since grand dad bought it from new, passing by dad (dad sold it to a unknown person who never took care of this beaut') and finally ends in my hands. I'm truly in love with this small warrior since it rolled out the dealership. Anyway, where I live each 6 months I have to take the truck to some emissions test so i can keep it driving "legally". The first time of the test got rejected due to blue smoke.
Indeed the truck got code 25 & 26.
As a first check, valve seals were worn-out but as I digged in more other thing we're damaged, so i changed piston rings, all gaskets and valve seals as well. After this, the truck was running good, even the cold start returned to normal and so the engine runs well. Second try of emissions test truck got rejected again, this time operator tells me it's running rich. So i checked spark plugs and they were black soothed, all of them. Checked Air Flow Meter (AFM) as a possible issue but all parameters of resistance are fine (according to toyota repair manual) so i checked fuel pressure thinking it was the gas regulator valve but pressure it's good too (according to toyota repair manual).
So i gave the truck a long run, check engine light turned on but engine was running smooth, this time with 2 new codes: 24 (intake air temp. Sensor) and 31 (air flow meter sensor) as well with the codes 25 & 26 (lean & rich fuel mixture) so i gave a clean to the AFM and the IAT sensor with carbuclean and give it another run and everything was ok but after a while, check engine turned on again but nothing wrong with the engine.
The AFM is ok as well the engine, even in cold starts and with A/C on, but sometimes after a hard hill climb or in small periods there's a strong gas smell. There are no leaks just the smell coming out from the exhaust but in small periods of run. Other thing I noticed while giving a quick test to the AFM if you give two full throttles it sounds like if the AFM stays wide open.
Sparkplugs are new and original Denso spec.

Hope anybody helps me to solve this issue that ties me legally with the truck.
Thanks in advance

 

If the gate in the AFM stays open, the ECU might be adding extra fuel to the mix! ...thinking more air is coming through the intake..

 

Exhaust leak upstream of the O2 sensor would cause that issue. If the O2 sensor senses oxygen it will send a low volt signal to the ECU and the ECU will keep adding fuel until the O2 is used up. Makes the ECU think the AFR is rich.
Look for any leaks around the manifold to head/air injection gaskets or the crush rings at the top of the downpipe. Also look for any cracks in the manifold or downpipe. Also, see if the O2 sensor is operating properly(test between E1 and O2 in the test box). Could even be a loose O2 sensor or bad weld at the bung.

 

check the engine coolant temp sensor, you can find the resistance temperature chart on line https://autoditex.com/page/engine-coolant-temperature-sensor-ect-13-1.html
The sensor makes a huge difference in how rich the engine runs