Weak idle

I have a 1982 Rabbit convertible with a 1985 1.8L MZ (Canadian version of JH I THINK) CIS. I just rebuilt the motor, and there's some quite old rubber on it.


So by weak idle, I mean revving to 2000 rpm, foot off the gas and it falls down to a stall. Also from 1500 rpm, it will drop below regular idle.
Regular idle is 1000 rpm.
A 5 minute drive tonight left a slight idle fluctuation, maybe 70 or 100 rpm.


I replaced all small vacuum lines with the rebuild.
The breather hose from the valve cover to intake manifold collapsed, causing excessive backfiring and extermey rough and poor idle. Replaced that.
There SOUNDS like a small vacuum leak coming from the 5th injector line, on the far passenger side of the intake manifold.
The rubber vacuum hose going from that cold start valve around to the the module on the back of the manifold is quite stiff. I sprayed lots of carb cleaner on the area and no idle change was heard.
 The injectors were leaking, so I got new injectors and O rings, but turned out to be the fuel plate rest position. So injectors are leak free.

The car sat for quite a while, I've run 3/4 tank of 87 octane through it. The door label says 91 octane (oops) but again, car is different than the motor. Anyways I'll run this tank through and see if 91 helps.
If anyone has any ideas, let me know! Thanks.

The 91 octane was RON rating system, that's 87 octane in Canada. I increased the throttle cable position screw by 1/2 turn and she runs great now.

The biggest issue that I have seen is that the RON or "pseudo-octane" Rating is just that.  I know that fuel trucks occasionally drop the wrong gas in the wrong pumps/tanks… and then add the Ethanol factor of 10-15 percent, that is what we call e-10, 0r e-15 rated fuel, and
it's a game of chance.  

They have stations here that sell un-ethanol fuel here it is about 75 cents higher than 91 octane, but it sure makes a Difference in how my 2-Cycle engines run.  

Kind of like my old Rover 3500s and 130 AvGas.  She loved that stuff, and ran really really well on it.
But that was 2 dollars a gallon when normal Ethyl was only 35 cents a gallon.