Sorting out a high, lumpy erratic idle.

[ianelvar]

My silver rex has idled badly since I bought it a month ago. I tried tuning it using the usual method for checking vacuum leaks and adjusting the bleed valve and the throttle stop screw. This didn\'t help. I noticed that once she was warm the fast idle cam was still holding the throttle open a bit, and if I moved it off the cam the idle pretty much sorted itself out with a bit of tweaking.

There is a wax valve that is supposed to extend when hot coolant starts to run through it, and push on a screw in the fast idle cam to push it off the follower.
The short video below will hopefully show how it\'s supposed to work.
Please see pics 7 and 8 for labels of where various parts are on the manifold.

To test a wax valve, remove it from the manifold by undoing the three machine screws holding it on with a short screwdriver, take the small hose off, and remove the unit carefully. Mark the extension when cold (pic 3), and then pour boiling water into the pipe (pic 4), and let it sit in the boiling water that spills out. You can clearly see the extension, as the shiny part that nearly doubles in length if the thing is working right.
If not, install a new one, tighten the bolts, but don\'t re-attach the water hose yet. It\'s time for the old bleeding procedure! Get a 2 litre drink bottle, and cut the bottom off. Remove the filler cap (not the AST cap), and put the upturned bottle (minus cap) in the filler neck. It should fit OK. Hook the little hose that you didn\'t re-attach up in the air about 3 to 4 inches about the top of the inlet manifold. Now, hold the bottle firmly in the filler neck and pour in some coolant slowly. You\'ll hear gurgling from the metal pipe on the wax valve. Keep going till coolant comes out of it, then push the pipe back on quickly and do the hose clip up nice and tight.

The screw that the wax valve pushes on can be set so that the cam moves to the off position sooner or later during warm up. Screw it in to make the idle drop sooner, and out for later. Don\'t unscrew it too much, or it can let the screw slip round behind the wax valve.

To adjust the idle once the engine is warm, first make sure that the fast idle cam has fully disengaged. You can do this by pushing down on the screw that the valve moves, and checking that the arm that the throttle cable pulls does not move while you push and release the screw. You can  then adjust the throttle stop screw which is by the linkage (labelled in pic1). This may be blanked off with a cap in the top as it is in the photo. Remove the cap with a small flat-head screwdriver, and you\'ll see that you can now get a screwdriver in to adjust it.
With the car running, unscrew it till it no longer has any effect on the throttle, then tweak it back ¼ turn. The idle may get rough now, but don\'t worry. You then need to screw the bleed valve in. This is a little tricky to get to, but isn\'t too hard with a small flat head screwdriver. You need to feed it under the intake elbow, on top of the little black catch tank, and through to the screw just under the bottom throttle plate (labeled in pic2). Turn it in all the way. Now the idle is probably a little low, so gradually tweak the stop and bleed screws in until you reach your desired idle. You may find that it\'s still a little rough, and at this point you can start moving one in, and the other out until you hit the sweet spot. You\'ll find that there\'s a balance that can be struck between the two that makes it run nice and even.

You may need to adjust the TPS afterwards, the procedure for which can be found here:

http://www.robrobinette.com/tps_adj.htm

This sorted out my intermittently high idle, occasional hunting, rough part throttle running, and rather jumpy response to the throttle being opened and closed gently at low revs.

HTH.

Another thing to watch out for is a sticky dashpot, which is over the other side of the manifold, and stops the throttle closing too quickly. Mine was completely jammed solid on my red car.