I've got a vacuum leak, need help.

[Jerrymc]

We're about to take the X on a trip. It's been running beautifully since I got it two weeks ago. I even got 19.8 mpg in mixed driving last week, so I'm hopeful for even better mileage on a longer trip. Here's my issue.

When idling in park or neutral the X idles smoothly at about 500 rpm. When I turn on the heater or vents, I get a click about every 10 seconds on the drivers side and the idle drops to about 250-300 rpm and then goes back up. If I put it in drive and hold on the break, it idles at 500 steady and there is no clicking noise. If I turn on the AC it idles along nicely at 500 rpm with no clicking noise. I know this has to be a leak but I can't tell where. Any ideas? My Haynes manual is been pretty useless other than telling to to check for leaks, but its the "click" noise I hear that has me puzzled.

 

[budwich]

I suspect its your AC compressor kicking on periodically assuming that you mean driver's side engine compartment. What are the actual settings that you are using???.... assuming you don't have EATC, the settings where the air flow indicators are to both the floor and head allow for AC to come on depending on where the temperature control is sitting... more red is less AC while more blue is more AC. As a result, perhaps your idle speed is insufficient for the momentary AC activity. However, when you actually switch to the AC setting (on the selector), there is enough compensation in the system cause it "knows" you are going to run the AC is a "continuous" fashion. Also, maybe your heater / AC controller / vacuum motor has a vacuum leak at a certain position.

 

[dogfriend]

I agree that the clicking noise is probably the A/C compressor clutch kicking on and off. This is very easy to confirm: just watch the pulley on the A/C compressor and see if the click corresponds to the clutch turning on and off.

I think you may have a bad IAC (idle air control) valve for two reasons:

1. Your idle speed should be higher approx 750 - 800 rpm in P or N.

2. The IAC should be able to compensate for the A/C compressor to raise the idle speed when the compressor kicks on.

I think that your IAC valve is sticking and not letting in enough air to maintain proper idle speed.

 

[Jerrymc]

Well, I can't find anyone in a 50 mile radius with an IAC valve, although I'm still not convinced that's the problem. It idles fine without the air controls set on heater/vent. I did take it out and clean it though. Budwich was correct, the clicking sound is the AC compressor clutch kicking in momentarily, so I'm leaning towards there being a leak in that system somewhere.

Any good hints on how to find it?

 

[Turdle]

There is a Black device, looks like a top hat, near firewall where 2 coolant hoses go to heater core, on one of the hoses. It is a coolant bypass valve, actuates when the blower is set to vent, heat or ac, check it and the vaccum line going to it, trace back to egr solenoid( branches off there). Also, check the vacuum lines at the vacuum reserve globe( front passenger fenderwell), vacuum comes thru there to the bypass valve and egr vacuum.

 

[budwich]

Your AC will click on and off when in the modes indicate as the system "cycles" between heat and cool to try and bring you "dry air" of the right temperature. In terms of AC, if your system cycles "significantly" when you specifically choose "A/C" or "A/C MAX", then there is likely an issue with your AC system beyond your idle issue. This can be readily checked with appropriate gauges looking at both your high and low pressure lines. Frequent cycling is usually an indication of low refrigerant... but not always.

In terms of your idle drop, I would think that perhaps this could be the IAC but maybe other conditions that are putting a load on your engine (ie. low battery charge, high current draw... stereo, fan, lights) are contributing to your problem. In general, your engine / computer should "respond" to some variants of idle but the discussion on idle has occur before including some concerns from me.... in my case my idle is too high (800-900). Yours sounds too low as the "spec." appears to indicate an in gear idle of around 600-650 which I take as pretty "normal" for most engines that I have been concerned with in my experience.