constant idle jump!

[24flys]

I've been trying to fix the idle jump on my 72. It will jump from 1-2000 rpms constantly at idle after it warms up. All the info I've read says that this is probably a vaccuum leak. I've changed every vaccuum hose and ends that I could find and also got a new rubber piece that goes between the auxiliary air regulator and the intake distributor. I've taken the throttle body off several times and re-seated it with silicone. The only thing I haven't done is replace the bigger hoses between the intake distributor and the intake manifolds, but these look good and they don't move so I figured ends aren't wore out. Has anyone ever had this problem, if so, how did you fix it! I'm running out of things to replace and I'm running out of warm weather too! any help is greatly appreciated.

scott

[John Rogers]

A few more places to check are the PCV valve and it's hoses, the vent/oil filler can and it's cork gasket, the vac hoses and the diaphram for the distributor, the springs inside the distributor. If you can get a mity-vac try checking the MPS and the decel valve to see if they leak. Last of all check the inlet plenum since they can actually get holes or cracks in the metal. I usually try the spray some carb cleaner around the hoses with the little red tube so you can direct it close. Good luck.

[Dave at Pelican Parts]

Try the "donuts" around the injectors.

Also try tweaking the idle mixture knob on the ECU. Count the number of "clicks" the knob makes so you can get back to where you started.

Look through Kjell Nelin's D-jet Guide http://www.914fan.net/djet.html, and Brad Anders' D-jet page http://members.rennlist.com/pbanders for tons more info.

--DD

[retro74]

Sounds like several possibilities:

Vacuum leaks around the intake manifold at the heads are common from loose bolts. A 13mm socket wrench is needed. Turn only 1/10 on each nut at a time. Don't overtighten. To get the nuts tight on the passenger side, you may need to remove the MPS mounting bolts.

Try to use some starter fluid with the engine running. The engine wil rev-up if a leak sucks the starter fluid into the engine.

You could have bad fuel pressure or injectors and it is not firing all jugs evenly. Check your fuel pressure with the engine running. I got my fuel pressure gauge from Sears (cheaper than mail-order since no freight) and I used a steel air valve (used from the Pep-Boys service dept) as the screw-on end connector. Hook the fuel pressure gauge up to the cold-start injector hose.

It could be a bad MPS with a leak in it. Check out http://members.rennlist.com/pbanders/djetparts.htm and all of the related pages for more information.

Ignition is possibly the problem if the points are pitted. Small arcs can occur that will alter the performance of the ignition. Make sure that the little ground strap on the advance mechanism is solid and not frayed.

Good luck.

Joe