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With 9VDC applied the valve moves. When the voltage is removed, it flips back to the 'rest' position. Wether is open or closed I don't know.
Shooting carb cleaner into it fixed the issue I had. Starting on a warm engine sometimes stalled and I had to start again.
My 2 cents. My car's symptoms were idle bounce plus very poor throttle response. I had a difficult time smoothly engaging the clutch and I couldn't blip the throttle on down shift. I tried a software fuel adaptation with no change. My son remarked that when I let get off the gas it was as if the engine died. This was all fixed using a pdt999 to do fuel adaptation.
In the long mean time I tried a fix I read about on one of the threads here. That is to clean out the epoxy blocking the set screw on the isv and increasing the unadapted idle gap. As mentioned above, the valve is spring loaded to rest against the stop. No matter how much gap initial gap I put in, I could not affect the idle. How is this possible? Here's my explanation.
On an unadapted car, the action, on idle switch engagement, should be to let the valve rest on the preset gap. Instead, The isv on early C4 is wired backwards. When the idle switch is engaged, this would send the valve to the complete opposite lock, closing the valve and causing the engine to shut down until the rpm drops to the point that the ECU tries to recover by opening the valve, in this case moving the valve in the opposite direction. No matter how bizzare this sounds this, behavior completely explains the symptoms I experienced. I didn't know they used pwm, but inverted leads would have the same effect, I believe.
I wanted to test this but never did. Now that I see John is digging into it, I am wondering if he wouldn't try to devise a way to see if there's some substance to my theory. I'm thinking it would require hooking an oscope to an operational isv.
I still have the modified isv if anyone is interested.
After I have made my test leads up and have an oscilloscope trace, I’m going to dig deeper into this, maybe even try to get to visual record of what’s going on in real time. I have a Dremel and I’m prepared to use it!
In the meantime, any scan tool outputs of other cars at idle would help
I already open the ISV years ago just to see "how it's made"
I got many pics of the autopsy
as you can see .. a lot of gung was inside the ISV ...
there is two needle bearing and an axle maintaining the vlave and alowing to rotate BUT one of both needle beering ( the lower one near the valve ) was almost frozen/rusted ..
probably due to moisture or humidity ..
thus leading to a almost blocked valve ... rotating VERY slowly ... of course leading to very slow idle adaptation ... to say the less .
I clean everything , antirust , some polishing on the "rusted" inox axle then OIL the needle bearing ....
reassemble all the parts and everything is runing VERY fine now ..
doing this on 3 ISV so far ( mine and 2 for pal )
I can easily capture some metrics/screenshot from scantool Or if you want form PDT999 that I have in my toolbox .
Great info. Merci bien. What ever scanntool and PDT999 outputs you can post would be appreciated. I think the PDT999 has outputs not in the scantool e.g. the duty cycle.
0x61CF = Idle RPM bump during start
0x61E0 = Idle RPM bump during restart
0x61D0 = Idle RPM bump when HVAC
0x6202 = Idle RPM when HVAC compressor running
0x620D = Idle RPM when Heat is turned on
0x6221 = Minimum CHT to use O2 @ Idle
0x7E5F = ISV Battery Compensation
0x7F8F = Off-throttle Idle Restart RPM (calculated)
You may have issues with the refresh speed if you try to view everything in scantool at the same time. And the external memory addresses listed above are only valid for the ECU with the following part number;
External Memory locations should be referenced via relative addressing so that everything works on different ECUs but that is not the case with any of the currently available tools.
Last edited by JasonAndreas; 05-04-2018 at 11:48 AM.
The official test lead
I searched the inter web for the VAG1315A test cable and based on availability and cost decided to build my own as it’s nothing more than two connectors and wire leads off each.
AliExpress supplied a Bosch EV1 female connector with wires attached and a male plug as well. I just soldered a couple of extra wires on when plugs.
To use it I simply unplugged the ISV plug and connected the test cable to the plug and the ISV.
I then connected the leads to a basic digital oscilloscope. That confirmed that the DME controls the ISV with a pulse modulated 15V signal. While the oscilloscope measures duty cycle (power going to the ISV) I’m going to try my automotive multimeter duty function as it may be easier to use.
dipalumbo -
i removed the epoxy from around the Allen screw on my ISV so I could see what change different settings had on idle. I found that by making small adjustments you could change the idle speed of the engine. I could increase RPM about 700 RPM or take it down to the point where the engine would stall. I was able to adjust the setting so I could get a fairly stable idle around 950 RPM.
One question I have about my set up. I have a 95 Varioram on my 964, but I have the stock 964 ISV (2 wire). Does it make any difference as to the type of ISV ( 2 or 3 wire) you run with the Varioram. I wonder if this is the reason that I have a hard timing setting a good idle. The spring load on the 2 wire may allow to much bounce for an even air flow - where the 3 wire may restrict movement and maintain an even/consistent opening for idle.
Just wondering. Then the next question is what are the stock settings for P, I, and D which control the response of the ISV.
More tinkering this morning. A while back, I bought an automotive digital multimeter with an inductive pickup so I could periodically check that both distributors were working i.e. check for bad coils or a broken belt.
It turns out that the meter also measures duty cycle (% time a signal is on / time a signal is off). This means I can measure the live input to the ISV i.e. I can watch the DME adjusting the ISV position to maintain the desired idle speed.
When you first turn on the ignition, the DME sends a short signal to the ISV (shows up as duty cycle of 80%), then it does nothing until you start the car. When I started the car it quickly moved to ~ 63% duty cycle. Blipping the accelerator didn’t change it until I released it, then the duty cycle quickly jumped to 80% and settled back to ~ 63% when the idle stabilised.
It was a lot more dynamic than I expected. I imagine this in concert with the idle map advancing the timing is what sets the idle. As a note, I thought the idle speed was set in the DME i.e. you can’t set it by changing ISV parameters.
I imagine this in concert with the idle map advancing the timing is what sets the idle. As a note, I thought the idle speed was set in the DME i.e. you can’t set it by changing ISV parameters.
No. I have a SW chip and my idle is actually quite good, even with a LWF, except when cold with air con on and coming to a stop. It stalls occasionally then.
Another NZ Rennlister has fitted the AliExpress one and reports that the idle is fine with it. Based on that I’ve ordered one as well. If nothing else it will give me a spare to fit to fellow 964 owners cars to implicate/eliminate ISV as the source of idle issues.
dipalumbo -
i removed the epoxy from around the Allen screw on my ISV so I could see what change different settings had on idle. I found that by making small adjustments you could change the idle speed of the engine. I could increase RPM about 700 RPM or take it down to the point where the engine would stall. I was able to adjust the setting so I could get a fairly stable idle around 950 RPM.
Hey Gus. That's really interesting as I visibly opened that gap considerably with no change. I should dig the thing out of storage to confirm. This supports my thinking that the wires were crossed and the %duty cycle John reports inverted. As the isv gap opens more it actually begins to close up again. So opening too far will result in complete shutdown.
Also, the spring return on the ISV I messed with was pretty strong. Not sure it would bounce.
John - That's what I'm talkin' about. Looks great. Do you have to do a fuel adaptation on your car after battery disconnect? If so I'd really like to see what the duty cycle is before/after adaptation. Also does increase duty cycle increase or decrease idle (open or close valve)?
John - That's what I'm talkin' about. Looks great. Do you have to do a fuel adaptation on your car after battery disconnect? If so I'd really like to see what the duty cycle is before/after adaptation. Also does increase duty cycle increase or decrease idle (open or close valve)?
I haven't adapted this car for a while, but interestingly another car I tried to adapt had exactly the same IAC trim showing on Scantool. Maybe adaptation isn't as significant as we think?
Re duty cycle, my longer video showed that it was settling at ~ 63% when happy and warmed up, stayed the same when the throttle opened and went to ~ 78% when bringing the idle up from a throttle closed position.
Logically, the duty cycle is important when the idle circuit is on, as the ISV bypass is the only source of air to the engine and it appears that more duty cycle = more activation = more air = more revs.
When my new spare arrives from China I'm going to put it apart, cut a view hole, put plastic over the hole and film what's going on. Why? Well it's about understanding what's going on with duty cycle so that in future I can insert my test cable, measure the duty cycle and help diagnose hunting idles etc.
05-03-2018, 02:46 PM
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