2 SLS, Insrtumental variable

[max2013]

hi everybody!! I am not very expert in eviews or econometrics. plz help me to solve some of my problem regarding instrumental variable.
I am finding the relationship between corruption and economic grwoth using baaro cross country analysis.
I need to find out one variable 'Investment to GDP' ratio, whether it is endogenous or not.

the model is

gdp growth= constant+ corruption index+ initial level of income+ initial level of human capital + investment to gdp ratio

since i am using gdp growth as the dependent variable and at the same time i am using investment to gdp ratio as one of my indpendent variable, that is why the question of endogeneity comes. i am using eviews for analysis.

I checked for heteroscadisticity. Now if i use "investment to gdp" variable one lag period then i think it will not be correlated with the residuals. now if i use another variable employment to gdp ratio ( or another variable which is population growth) and one period lag of investment to gdp ratio as the instrument for investment to gdp ratio and find out the 2sls model..is it ok???

then i check for the endogeneity of the variable investment to gdp ratio and i can reject the null (( the null is endogenous variable is treated as expgenous)), then can i say that my variable of investment to gdp ratio is an exogenous variable.

Thanku u for ur support.