idle at +/- 2000 rpm

91
4.0
4x4
ax-15

My idle is fluctuating between 1000 and 2000 rpm usually closer to the higher end. Its been like this for a while and seems to be getting worse. with smog coming up soon I guess I need to do something about it. I can sometimes get it to drop a few hundred by doing a light brake stand but at the next stoplight its always something different, usually 1500-2000 rpm.

about a year ago I replaced the IAC from vatozone, pulled a new looking TPS from the junkyard and can of seafoam between the TB and booster.
no change at all at that time.

What else should I look at?

Im planning on getting a new TPS and IAC again, and not sure what else may affect the idle.

It sounds like you have a vac leak, what I'd do is get a can of starting fluid and spray it around where the head and intake meet and to check for leaks.

yeah, I did put an APN on it a few years ago so its possible. ill get a can of starting fluid tomorrow.

Check for vac leak and faulty TPS.

I didn't get to it today, stupid busy day in Comcastland and I'm beat. Tomorrow doesn't look so great either. I'm off Sunday so i'll git er done then.

looks like vac leak is the culprit. when I spray the back of the intake on the underside, the idle drops and just about dies. stop spraying and right back to 2 grand.

I guess I need to grow some gumby arms and get back in there. hopefully the gasket is still ok, probably not with my luck but I can hope.

I had this problem some years ago with an 89 XJ, I found this issue largely cleared up when I cleaned the IAC with some brake cleaner. I would have to re-do it periodically.

It isn't that bad of a job to change the gasket if you are double jointed and weigh about 60 lbs. irate1: Just remove all the bolts and pull the header back enough to slip the gasket in. No need to actually remove anything.

Before you do anything, tighten all the manifold bolts and see if the problem goes away. It is real common for the rear stud to break off so check for that as well, of if need be you can have a drill and an easy out available. IIRC you might need a right angle adapter on the drill as well.

Just a hint.....Get a can of spray coppercote and cover the gasket on both sides before installing. It really helps keep the leaks to a minimum. Whoever came up with the idea that the material for an intake manifold and an exhaust manifold should be the same should have their head examined, then shoved up their arse.

The intake has dowel pins and when the dowel pin doesnt sit in the hole on intake it will cause vaccum leak

jeepguy72987 said:

The intake has dowel pins and when the dowel pin doesnt sit in the hole on intake it will cause vaccum leak

Click to expand...

I agree that is a possibility here. But usually it is such an extremely high rpm that you can't even keep it running. But I imagine there could be variation in symptoms.

Work/life has kept me stupid busy over the last few days and fixing it hasnt happened yet. I put a new gasket as well as the coppercote when i put the APN manifold on it and have checked the bolts I could reach a few times. If I ever get a day off again I'll gumby up and get back to them last bolts.

so a long overdue update (and repair).

The gasket I put in when I had it apart last time was an autozone special and didn't fully make a seal around one of the intake ports.

I put in a felpro with a good coating of coppercote and it runs and idles like new.