I am starting to go out of my mind trying to find my vacuum leak. I am having a very inconsistent idle. When the car first starts it idles fine for a minutes and then begins to hunt. I have posted on this before and had some good suggestions, but have found no answer. I have replaced all vacuum lines, fuel injector seals, intake manifold seals, throttle body seal, intake runner boots, checked the intake plenum for cracks, checked the dwell and timing, and the valves have been adjusted. The only possible leaks I can find is a hissing from the air screw on the throttle body and I noticed the cold start valve gasket was not the best when I removed the valve to check the intake plenum for cracks. Could one of these be the cause? Any other ideas. This is getting very annoying.

I went through the same thing several years ago; I installed a vacuum gauge.As you test various suspected leaks, you can see if there is a change. It also may not be a vacuu,m leak--this has been covered in previous threads as infintum

How much is it hunting? midway between cold and hot there should be some.

After the AAR valve is warm and open the engine usually hunts alittle (+/-100) until its hot.

It is hunting a lot. It will almost stall sometimes and then go up between 1000-1200RPM. THe odd thing is sometimes it will also settle in and idle rock solid around 800RPM but only if it sits. IF I drive and come to a stop it hunts again.

Ok, then I would squirt lightly some carb cleaner around the engine until I found the leak. Gotta be somewhere in there.

I know it is somewhere, just driving me nuts, I will try the cleaner later today and see if I get any results. If it idle as nicely as it runs when driving, the car would be great.

Spray just alittle bit on say one intake manifold sealing surface, wait....wait. Then try the seals area, wait....wait...
because if you spray alot it will fill the engine bay and raise the idle speed giving a false reading.

I am suspicous of the air plenum. I had leaks in mine. You have the throttle body on top and the air cleaner. All this can lead to pressures this way and that. This could cause an intermittent leak. There is also some space under the throttle body that is hard to see. I sealed the top of mine with excessive amounts of RTV. Worked for awhile. I have put a different one on since then.

Is it D or L jet? Just wondering if you have checked fuel press. or the MPS yet?

I have not tried this, but somwhere I heard that there was a way to test for leaks other than with carb cleaner. Carb cleaner supposedly is messy.

Can pressurized propane be used for the same effect, like from a portable torch? Or just air from a compressor? Would directing these at a leak site vary the idle speed too and ID the leak?

Have you replaced the oil filler seal?

I checked the intake plenum for leaks when I removed the intake manifolds to change the gaskets I removed the plenuma nd checked it. I have also replaced the oil filler seal and rechecked it yesterday and it was fitting well. I guess I just have to start spraying the carb cleaner. Next weekend's project. Thanks for the suggestions. Sooner or later this thing will run properly. I am starting to wonder if the computer has an issue, becasue if I adjust it to the fully rich side things smooth out and then if I back it off a few clicks it runs fine for a while and then issues again. The fule pressure and MPS are fine.

The best I have used is starting fluid...but people give me a rash of Sh*t for recommending it.

Carb cleaner works too and isn't as flame happy.

Propane scares me as its a heavy gas and quite flame happy.

The adjuster is a pot. There may be clicks but it is simply a pot. Maybe it is a "noisy Pot'. Can you borrow an ECU from someone? Are you handy with a soldering Iron? Installing a new one should be easy.

The clicks on the ECU should be from the case. It has notches on it. Clicks are normal. And from you talking about a knob on the ECU I am assuming you have a D-Jet car.

Also, have you checked Air fuel ratio yet? I would think if you had a vac leak, you would hear it. If your mixture is off, it would cause similar problems to what you are experiencing. Mine did the hunt thing for a little while until I richened it and made sure my timing was dead nuts on. What ECU # do you have? Do you have the correct CHT to go with it? Does it require a 270 ohm resistor like mine? I have a '73 2.0 with the correct computer/mps/cht and it requires a resistor. Just a thought.

mine does the same thing and I have replaced all of the items that you mentioned, I have a 73 2.0 with D jet...I have not begun to dig into the idle issue, I did buy a new set of wires to see if that would cure the problem...my car starts up nicely, the car idles down when warmed up...then will hunt from 800 rpm to 400 rpm, then bounce back and forth...then occasionally when stopped it will be rock steady on 800 rpm...I am hoping the wires will cure this problem.
Joe

I would hope that new wires help you, but I will tell you I have new wires, plugs and points in mine as well and still issues. I am sure I have a leak somewhere. I just need to find it.

I am having a high idle problem. I want to seal the injectors and the intake manifold gasket. Has anyone used RTV Blue to seal the gaskets around the injector ends and the intake manifold gaskets? I can hear a small leak at the injectors so I think that is where the problem is.

No, I just use new O rings and gaskets as they are dirt cheap.