So I’ve recently purchased a 1990 Toyota pickup 3vze manual 5 speed and it has been great it drives really well but I am stumped as to why it surges in first gear. It only happens when accelerating slow. I’ll be driving smooth then about 1300-1500 rpms it seems to lose power and then get some out of nowhere causing a small surge that jerks it forward and then smooths out. Only happens at that spot and only while engine is warm. I also am not able to pass smog with this problem because when I go to hold the rpms between 2000-2500 it jumps. I’ll rev it nice and slow and it’s smooth until 1500 where it will start to kinda jump up and down about 200 rpms. Then when I add a bit more gas it jumps straight past 2500! Im thinking it’s some sort of air or fuel delivery issue, but don’t know what I should check first or maybe it’s an evap leak. (Side note: check engine light has come on twice then gone away shortly after)

 

I would start by checking your fuel pressures to see if it's fluctuating when you're having the issue

 

So the solution turned out to be super simple!! Messaged my cousin and he suggested cleaning the throttle position sensor! And so I took off the throttle body and sensor and everything seemed pretty dang clean! So when I put back the throttle sensor it had some room for adjustment so I put it open a bit more and it worked, no more surging and passed smog perfectly!