can't get idling RPM down

[Carlos]

Hi,
I am currently working on closed loop idle control.
For idle control I had PWM warmup set up. Not really tuned in finally, but OK to take off and take a cruise.

Now I thought it is time to finetunetune it. I am looking for closed loop as this is very helpful with my auto transmission which drags down idle RPM if engaged.
For my Bosch two wire, I use 1kHz, 25% closed - 90% fully open, tested with output test, works well.
After starting the cool engine, I can see that PWM% step by step decreases down to where the valve is closed.
However, the engine then still revs around 1.100 RPM, which is far too high.

Before fiddling around I did a simple test with warmed up engine...
I closed the intake of the idle valve, so no air can go in there. Then I adjusted the idling RPM of the engine to 650-700 RPM by slightly opening the throttle bodies ( 8 x 48mm, well synchronized) by idle screw. Engine is idling well w/o using any idle valve.
If I now open the idle valve intake, but having the valve itself closed (PWM 25%), the RPM immediately is increasing by 350-400RPM.
There is nearly no room for further closing the throttle bodies, the opening gap is not even visible.

I thought I might play with the ignition retard during idle, or even reduce the intake of the idle valve by a plug where I could play around with different diameters, but before doing so I wanted to ask you for your opinion.

Any hint aprecciated

Thanks
Carlos

[omniserv2]

Hello, I'm far from a expert here, but I did just finish my Datsun 280zx project. I to had a fast idle with my throttle completely closed. I found on my engine that there was air getting in the intake by going around the throttle body with a bypass hose. This hose was part of the OEM emissions BS. I pulled and plugged the OEM emissions hoses and than was able to dial back the idle with the set screws on the throttle linkage.

The way I looked at it is there is no way the engine could run at 1100 RPM's without getting the air to do so. So some where it's getting air.

Best of luck.

[kaeman]

I am thinking vacuum leak also...... if you got it to idle at 650-750 warm blocking off the idle air valve, then unblocking it you have 1100 as you lowest idle, then I would look at the valve or the hoses for a leak.

[hardline]

25 seems high for closed. My 2 wire idle valve cracks open at 18%

[Carlos]

I carefully checked the valve...
The Intake is big enough so I can see the moving disc, which I marked with a red dot to see where end positions are. 25% and 90% are the values forclose and open.
However, If the valve is fully closed, I easily can blow through it. There is a difference between cosed and open, but it definitely does not fully close mechanically, even if it is at the closed position, there is a basic opening which seems to be very big.

Does anyone of you have a PWM 2 wire valve which is really closing ?

Carlos

[hardline]

My 2 wire valve stays sealed when unplugged. Won't leak air or liquid.

[Carlos]

My 2 wire valve stays sealed when unplugged. Won't leak air or liquid.

Do you have a brand and partno I could use for ordering ?
The one I have is a BOSCH 0 280 140 516, bought brand new but crappy.
Txs
C.

[hardline]

Where at in the world are you? The part I use is a USDM Ford part. You'll need to make a mounting plate for the vacuum side of the IAC. My manifold has a flange for it, so this is why I use this type of IACV. It is OEM for the Ford 4.6L Romeo V8 from the Crown Victoria Police Interceptor. Ford part number is 2W7E-9F715-BA

[Carlos]

Where at in the world are you? The part I use is a USDM Ford part. You'll need to make a mounting plate for the vacuum side of the IAC. My manifold has a flange for it, so this is why I use this type of IACV. It is OEM for the Ford 4.6L Romeo V8 from the Crown Victoria Police Interceptor. Ford part number is 2W7E-9F715-BA

Thanks a lot, I looked it up and I like the flange, makes it easy to mount on a custom made plate.
I'll ask my OEM parts dealer to get it for me.

Carlos (germany)

update:
Dealers can't get it over here (@ resonable cost and time), so I ordered it at www.rockauto.com, US$ 108.-

(it is also listed as IAC Motorcraft CX1783 )
MOTORCRAFT CX1783 (IAC)
FORD CROWN VICTORIA (2003 - 2005)
LINCOLN TOWN CAR (2003 - 2011)
MERCURY GRAND MARQUIS (2003 - 2005)

[Carlos]

My 2 wire valve stays sealed when unplugged. Won't leak air or liquid.

Hi,
received my Ford valve today, seems it also stays open slightly. ( tried 18 & 99 )
@ what frequency are you running it?

txs
C.

[hardline]

I run mine at 1khz, i cna fill the chamber closer to the solenoid with a liquid, and it will not drain into the other side. Do you have the flyback diode installed across the IAC wires?

[Carlos]

Txs for the data, I tried 1kHz and I do have the flyback diode installed.
However the valve doesn't fully close. It remains mechanically open (
Guess I will go to the junkyard and see if I get something else.
C

update:
got another used Bosch 2wire, running now 34% closed 70% open @99Hz
what I observed with this one is the fact that w/o voltage applied it is slightly open as well.
Increasing voltage closes it at 34% then continuously opens until 70%.
Should work now. I'll do some idle adjustments at the weekend.

C.