Idle Air Control Valve (IAC Valve) cleaning (possibly)

For ****s and giggles, I destructively disassembled my old IAC valve. Verdict: No user serviceable parts inside.

Well, not unless you a retired German machinist with a shop and lots of spare time. Anyway...


It's a dry valve, and looks like it's susceptible to carbon fouling from the occasional backfire(?). My valve was a bit dirty even after I had run TB cleaner through it.

It appears that if you were to blast it with TB cleaner, and then saturate it with a good penetrating oil (that leaves lubrication, I wouldn't use WD40, better would be PB blaster or other), it might resurrect a poorly functioning IAC valve.

Better would be to clean/lube while giving it 12V to open/close the valve. Possibly even to use MMO or synthetic motor oil for lube.

Anyway, I'll probably pull mine every couple of years and give them a clean/lube.

That's my $0.02 and I'm sticking to it.

 

note that if you have a LH2.4 car (eg, 1989+), with the diagnostic box, there's a 'DTM-3' that will cycle the idle control valve (along with other actuators), which could aid in this.

 

New to me, and I just searched the forum (no reference to DTM-3).

I'm guessing there's some sort of diagnostic mode where it runs the various actuators when the car is off, so you can check them? If so that's sweet. Pray tell!

 

DTM1 is where you read any stored codes via LED blinks, while DTM-3 is the actuator test I mentioned.

Engine and OBD Diagnostic Codes

 

When I had my 740 GLE mine went out with about 1,500 miles on the car. The dealer just swapped it out.

 

Pierce, how do you access the DTM-3 feature? Didn't know bricks could do this.

 

see that link above.

 

Thanks, missed that link.

 

Dang, must have browsed that page half a dozen times, missed that part entirely.

Despite the fact the bugs aren't quite all swatted with this particular brick, somehow I feel smarter for owning it.

 

More on the IAC, and why you should clean your TB regularly (so you don't have to clean your IAC, bold and underline is mine...)

Excerpted from Engine Tune and Performance:

"The fumes from the breather are carrying oil and combustion vapors. When this stuff attempts to past the butterfly in the mostly closed state, the pressure (and hence temperature) drop causes the fumes to condense out of the air stream... sticking to the walls of the throttle housing right around the butterfly... a petroleum snow storm. As an aside, this buildup can cause really weird problems on cars with automatic IACs (idle air control: idle speed control). The gunk will restrict the air flow through the butterfly, forcing the IAC to open farther to maintain a proper idle speed. On some cars, you end up with the IAC operating well outside it's designed range... resulting in a major ring/hunt. Killer surging. Oh, and since the butterfly is plugged, all of the air, and breather fumes, pass through the IAC. The snowstorm happens in the IAC, ruining it. Do NOT adjust the throttle stop! Clean the gunk out. 30K is about right for a XJ40. Every 15K or less on cars without a heater... BMW, Volvo."

 

what bugs me is, the crankcase breather on the turbo is upstream from the turbo. so that gunk is being blasted through the turbo, across the intercooler, then through the throttle body to the intake. that spooge must make a mess in there.

the 92+ turbos at least do have a heater on the spooge pipe into the intake. this heater comes on with the ECU.

 

Why not move the breather to another location?

Another option would be to put a gunk collector. I did this once on a Ford Taurus. It was blowing considerable (due to normal engine wear) oil through the breather.

I took a small juice can, cut hole in the top for a short pipe, and cut the bottom out. I filled this with BBs and put a screen over the open bottom to hold the BBs in.

I fixed this to the top of mayo jar so the pipe was sticking out. I put another pipe next to it for the return.

Dirty air flowed into the juice can, condensed out, and fell to the bottom of the jar. I would empty it when it started looking like it might get to the bottom of the can.

It collected sh!tloads of sludge which I would dump out periodically.

Now that I think about it, that's probably not a bad idea to do to these current bricks.

I toyed with making one out of steel/PVC so I could put a petcock valve in it to aid sludge removal, but never got around to it.

 

You can usually find cheap oil catch cans on ebay, most with the clear oil level tube. But usually they are sealed up so you couldn't add a screen or filter without cutting it open. Would some kind of filter be that beneficial? Wouldn't you have some other issue if you're getting more than just small amounts of oil (maybe more depending on the vehicle) through the breather?

 

Slim,

The Taurus I installed it on had 150k+ miles on it and used considerable oil (qt/1000 miles).

Personally, I'd rather catch the crankcase oil residue/gasses (the BBs supposedly allow better condensation) instead of trying to burn them in the motor.

Peirce has noted that the crankcase breather on his turbo brick is upstream of the turbo, which isn't exactly desirable.

 

well, you can't put it downstream of the turbo as that is positive pressure when you're on the boost

 

I'd either buy or make a catch-can. Solves the problem, least modification.

 

where does that catch-can vent the nasty fumes?

 

Nasty fumes go where they always went, but it's not the fumes that are gunking things up - It's the gunk (fine oil/air droplets with carbon) that's the issue. I think these get sent into suspension in the crankcase/valve cover by mechanical action from the crank/cam and mix with exhaust gasses leaking around valves/compression rings.

My can used to routinely catch 1/2 cup of black sludge with a brownish foam on top between fill-ups. IIRC I tested it and it reacted with baking soda (yikes). However, that motor was a '96 3.0L Ferd Tourass with a lot of miles on it (for that car). It served us well, but we used it up...

 

"The contaminants are oil droplets from the crankcase ventilation system. Every engine generates some blowby (gases blowing past the rings) - especially turbos. When the crankcase ventilation system routes these gases into the throttle housing, they carry oil residue with them. "

Via Engine Tune and Performance

Mmmph.

I'm making two catch cans this weekend...

 

Turns out I'm not the first one to try and clean an IAC

Engine Tune and Performance

I had tried to clean the IAC on my Regina brick (which started surging and hunting soon after my Bosch brick), and experienced the persistent high idle issue. Thought cleaning the IAC caused the problem.

Looks like I probably didn't. It almost seems like the spring in this IAC is too strong, as when the valve opens, it opens all the way. Maybe something with the solenoid.

Anyway, going to go cut the plug off a Bosch junk car and splice it into my Regina car, to see if I can run a Bosch IAC on a Regina car.

Stay tuned...