01 tacoma throwing code that says lean on side "a"

What could that be...I tuned it up about 3 months ago and about a month and a half ago I had a timing belt and water pump put in it by a guy that I trust to do my work....
about 2 weeks ago I started it and it started fine but then it started sputtering and almost died and I had to push the throttle and rev it up. Then it started running dine then did it again as soon as the rpms started coming back down...so I pump the throttle again and it cleared up....but as I was driving down the road it would accelerate at all...barely would go...but as soon as the temp gauge shos that the truck has warmed up it runs fine...my first thought was air filter so I cleaned it and it still done it....then I ran a can of sea foam through it and it still does it...it finally threw a code yesterday saying it was lean on side "a"...any thoughts

 

I would really help if you added the actual code number.

 

sounds like injector issues to me