Engine is a p72 Gsr with a t28 turbo, 650cc injectors tuned on hondata s300 at 8psi. Has a new distributer and plugs. I'll attached a video of it idling hopefully someone has some ideas I've been chasing it for about a week

 

 

Could be IACV, fuel pressure, a lot of things.

If the car has been "tuned" then the presumption is that this wasn't happening before and has only been doing that recently. Any changes between tune time and now?

 

Car had a slight misfire on the dyno but only at idle and was assumed it may be a bad distributor, I replaced it and it's still there. It has got slightly worse in the past week since I've replaced it but I have good spark so I assume it's a fuel or vacuum issue.

 

It's a bit hard to hear in the video and I don't have the best headset available right now, but based on the idle behavior I would suspect a vacuum leak.

 

Vacuum leak, low coolant level, bad spark plugs?

 

Vacuum leak still seems most likely to me just based on it's behavior. I've pulled some absolutely atrocious looking plugs from 25+ year old cars that have had minimal maintenance done on them, probably 150K+ on some cheap plugs, and while they obviously weren't optimal they never impacted the idle or caused a fluctuation like this.

Low coolant is an interesting thought and would also impact IACV, if OP hasn't checked that.

 

I will check the coolant level this afternoon, I did notice that the upper rad hose seemed to have vacuum on it when I was checking compression. It basically sucked it self closed at some points, When i looked a week ago it was definitely full of coolant.

 

Even the reservoir being full, make sure the system is Air-bubble-free. I've had quite a few times where I would think something is wrong by way of a vacuum leak or IACV, only to find that coolant in the system was low. Once filled, the intermittent idle went away immediately.

 

Checked the coolant and its all good, out of curiosity I replaced the rad cap and it cleaned up my idle still a slight bobble but not nearly as bad as it was. I haven't had a chance to take a boot around to get it warmed up real good yet. Definitely confusing, any idea as to why it would have been the rad cap?

 

Back to doing the same thing again today, (the stutter that is, not the suction on the coolant hoses). Gotta find some time to take the IACV apart and clean it, I guess that would be my next step.

 

Super easy, takes like 5 min. 10 if you've never done it before and you fumble around for your tools like I normally do.

Spray carb cleaner on/around all the vacuum lines, anything leading to the intake manifold or to the head. See if you find any leaks.

Edit: Left a comment to check AC compressor clutch, then realized you have no AC.