87 xj 4.0 idle problem

What I have... 87 xj 4.0 5spd 165k. BTW I just got it.

Problem.... This thing idles rough/ low.Rev it up alittle and runs great nice and smooth, let off the gas and she idles way down for about 30 sec or so and then revs back up to normal for about 30 secs.Also I have no power brakes at idle, or while reving in neutral.


What Ive Done..... 1. Chk all vacume line routing they all seem to be right, found a brake in the vac line to heating box, repaired. 2.Have disconnected the egr and pluged it.No changed. 3. I move the egr with a screw driver while running, to open it, Got way worse. 4.Tried a different Fuel pressure regulator.Same
5.Chk throttle body, it is pretty clean, no oil in air box. 6. While air boot was off ran and plugged Idle control valve, almost killed it. 7.Sprayed the whole itake system down with carb cleaner while running top chk for a vac leak, none found.
8. chk the valve at Brake booster working.. 9. played with tps ajustment.turning it changes the itle but after 30 or so It gose right back to low rpms.


I feel it is rich at idle,it smells rich.Note my ex manifold is crack near the o2 sensor.Is it poss that the manifold is sucking clean air in on the o2 so the o2 thinks its lean and richens it up?I dont think it is any kind of injector or ign problem because of how smooth it runs.I am going to get a MAP and ICV and egr control valve tomarrow and try them.Is it poss I have bad Brake booster causing this??

I think if you have no power brakes at idle, you still have a vacuum problem. Perhaps the brake booster itself, or perhaps intake manifold or throttle body. You might begin by disconnecting and plugging vacuum taps on the manifold, including the brake booster, to see if there's a change. But even a sick engine with minor vacuum leaks should give you some boost.