High idle ITB

Hello all.

I'm working on my PSA 1.6 16v engine with gsxr1000 ITB's.

I previously had kawa zx14 bodies but they seemed to be a bit too big with 46 mm. Those are 90 mm bore spacing as well an my PSA is 84. I had a hard time modifying them to 84mm spacing and therefore the quality of my setup was not too good. I basically had to choose between sticky throttle plates or 1500 rpm idle.

I decided to discard them and got a set of gsxr1000 k2 bodies. Worked far more on quality this time. These are 80mm spacing standard but I made spacer rings of 4mm on the lathe so it's bang on 84mm and straight as an arrow now.

But surprisingly, I have a high idle again. Still have to shut the plates almost 100% to get down to 1200 and then no room to sinc them. And again sticky plates. I tried quite a lot of ignition advanced idle control and the ecu is trying to get the rpm down with very late ignition, but it's not enough.

I tried Speed density, Alpha-n and alpha-n with map corr. but it doesn't make much difference. I have a vacuum manifold just for the brake booster and there it's barely 70 KPA max vacuum.

Should I again be chasing vacuum leaks or can this be something else? Can one say that if you have to force all 4 valves shut to get down to 1000 it must be vacuum leaks? The only thing left I can check is the O-rings of the bodies themselves.

BR Arthur

Find the vacuum leak.

GSXR 1000 throttle bodies (K8 series in my case) have a built-in stepper IAC valve. Have you blocked this off, as well as the port for the MAP sensor?

Are the plates closing fully and equally. It only takes a little bit of leakage to affect an idle. Hold them up to the light and see how much area is showing. Maybe work on the position of the plate in the bore if necessary

K2 do not have a stepper for idle. Only for pre-throttle plates, yet I removed this. Indeed now I have removed the bodies again, and I look into the light, I see a slight difference in light coming trough. It's not much though.

The point is (now) I can't really get them fully closed and equal at the same time. If I remove all sinc springs, all valves are closed, yet not equal vacuum on the carbtune. When I have equal vacuum, one valve is more or less forcing the other to open a bit. Maybe this proves one is still leaking at the o-rings.

I will get new 2 mm o-rings today. (previously 1.5mm). I will get them back on the lathe and increase the grove I made to fit 2mm o-rings.

Thanks