old_man said:
Troubleshoot by eliminating possible leaks. First pull and plug the vacuum hose to the brake booster and check the idle. If that isn't it, reconnect and proceed to check all the vacuum lines leaving the intake manifold. There is a common problem with a busted plastic hose that runs to the bumper vacuum canister. It breaks roughly under the battery. The carb cleaner technique works, but you have to be carefull not to loose your eyebrows. I learned that the hard way about 40 years ago.
There are numerous possibilities for vacuum leaks. I just troubleshot one for a friend where the EGR valve was the problem, so take nothing for granted.
Funny just noticed the other day, a surge at start up. Noticed it changed with the setting on the heater controls. No surge with the heater off, what next?
Just on a hunch, awhile back, I cleaned my MAT sensor, manifold air temp. idle changed and seemed not to want to hunt so much.
Might want to have a look at the throttle stop and the TB butterfly valve, possible somebody could have messed with it in the past and your cleaning of the TB, loosened up the IAC enough, to mess with the last throttle/butterfly adjustment. Adjustment of the throttle stop, messes with the TPS setting, just take a look and see if there is much/any gap between the butterfly and the wall.
TPS sensor adjustment seems to have some bearing on idle, at least mine changes some after an adjustment.
If you unplug the C-101 plug you are opening a worse can of worms, than the intake manifold. I´ve found it easier to unplug everything upstream of the connector and downstream of the connector and test for resistance through the connector. I removed one and cleaned it, never again. Only a few wires go throught the connector, that can mess with your idle. I have an extra wiring harness, that I lay out on the garage floor, along with a good wiring diagram, it makes checking the harness IN the XJ, much easier, by following and looking at the destinations on the garage floor. Primative but functional.
On a hunch, check the wires at the front end of your injector rail, that go down the front and under your motor to the knock snensor, O2 sensor and temperature sender (for the computer). Often find them frayed and/or cooked on the exhaust manifold. Could account for the idle going up with the temperature, it´s usually just the opposite, starts high and then goes lower.
You could be right about the intake, possible when it heats up it leaks worse. A cracked exhaust manifold, has also been known to possibly, affect the O2 sensor and idle, had one with high idle, after changing the exhaust manifold that idled lower, but then again, it could have been the gasket. Have heard from some guys, an exhaust manifold crack, can have a venturi affect and actually suck some air under certain circumstances, sounds logical, who knows.
If the O2 sensor is getting extra air, the idle is going up.
Last tip, if you do take the manifold off, have plan for dealing with some exhaust manifold cracks, can´t remeber taking one off, without finding at least a little crack someplace. I always take off the heat shields and throw them away, newer XJ´s don´t have the heat shielding and next time, the manifolds are a whole lot easier to remove.