1999 3.4 engine harness and ECU in a 1993 Toyota 4Runner originally a 3.0, all wired up correctly. My question before I go and try to start it again is why did it backfire through the intake so loud that my neighbor came to check on me lol. The last components needed was the MAF and intake, I got that in the mail and was quick to put it on, before installing these parts I was able to start the engine and it would run for about 2 seconds before shutting off obviously cause of the unplugged MAF and no intake. After installing the intake and MAF I tried to start it and it backfired so loud it made my ears ring. I’m worried to go and try starting it again. I noticed a rather large crack in the bottom of the intake, my question is could to much air getting past the MAF, almost closed throttle plate due to my throttle cable wire being adjusting incorrectly, or MAF being to close to the throttle body cause the massive backfire? Any input is appreciated!!

 

the only way for a backfire to occur is to have fuel and fire in the intake at the same time, so valve and spark timing or a bent valve are things you should look at that would allow spark or burning fuel from a cylinder to ignite the air/fuel in your intake.

 

 

possibly, did you use a lot? it generally evaporates quickly, but if your throttle body was closed it may have still been in there and some was still burning in one of the cylinders when the intake valve opened causing the backfire.