The book way is for the computer run carb 258 engine. At 1600 rpm, your
mechanical timing is full advance and then the computer takes over. I
believe the distributor vacuum line should be off and plugged too.

My guess is that click you hear shutting off the vacuum leak (high idle)
is the defective PCV/canister solenoid that sits just behind the carb.
These never did work, so the fix is to pull it and just put a plain T
fitting in it's place.

My CJ7 with no computer messing up the works runs best at about 7-9 deg
advance at 700 rpm with a ported vacuum signal. But, when I killed the
computer, my timing had to be advanced by about 10 degrees to run
manually.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Joe and Joann wrote:
>
> Thought I would check my ignition timing on the 1990 256 YJ. Checking at
> 700 rpm showed only about 3 degrees advanced. I advanced it to 9
> degrees. I had to back the idle screw almost all the way out to get it
> back to 700 rpm. The strange thing is that now after letting off the
> gas, the idle is very rough and about 300-400 rpm higher. After a
> varying amount of time 5 to 20 seconds, the idle drops to about 700 and
> smooths out. When the idle smooths out and drops to where it should be,
> there is a click somewhere on top of the engine. My guess is that it is
> a solenoid. Anyone know what the computer might be doing after coming
> back from high rpm to curb idle. It doesn't seem to be the sol-vac that
> is doing it.
>
> The good news is that the Jeep is way more responsive and has never run
> better. If I could just get rid of the rough faster idle period I would
> be a happy camper.
>
> I have checked several times for a vacuum leak and so far no luck.
>
> Also I am somewhat confused about the procedure for timing adjustment in
> my Haynes book It says to disconnect the electrical connector from the
> CEC sys switch located on top of the valve cover. What is this? It also
> says to increase the idle speed to 1600 rpm and the the timing mark
> should appear stationary. Does this mean that there should be no advance
> between spec idle at 700 rpm and 1600 rpm? It seems there was some
> advance on mine as you went to 1700 rpm, which I attributed to the a
> centrifugal advance. When I checked and reset the timing, I only
> disconnected the vac advance, but not the CEC system switch since I
> could not find out what that was.
>
> Guess I am missing something here.
>
> Aloha from Maui
> Joe