Okay so some of you know a while ago I bought a 91 ef hatch stock d15b1 and its treated me well except for lately i've noticed that when I turn my heater on my motor will surge down then go back up and usually during idle my cars idles up and down. I've also noticed when I slightly step on the gas in neutral I can here it surge down for just a second almost if it were missing. What the big thing for me is while I'm driving and the car is not warmed up all the way I'll shift to neutral to stop at a stop sign and as soon as it goes to neutral I can feel the engine surge way down almost as if it were to die. But when my car is warmed up and been running for a while it usually wont do this. I heard it my be I think the Iacv or something? I just want it to run properly before I get my b16. Please any help will do its my only car and daily driver. Thank you! Oh and idk if not having a catalytic converter would also be a factor. Thanks everyone

 

Check, in the radiator not just the plastic tank, that the cooling system is full. Clean the IACV, if it's a DPFI system it is on top of the manifold near cylinder 1.

 

Okay I'll check those out. Its also not throwing any codes or check engine light. Could it be the map sensor?