The Project Pad

Yup, 10-12 hr shifts in auto-industry with a decent commute, besides the unsociable hours it's good in some ways, against traffic coming to and from work with a good crew to work with. Having a bit of daylight to play with before work is great too.


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I work 12 hour shifts at night (for now), but I also sleep at work! This kind of schedule can be tough, but sometimes you gotta work hard for the money!

Sorry I don't really have any input on your situation for now. If the VEMS output can only operate at 250 Hz, that would definitely impact the functionality of a valve which is meant to be operated at double that frequency... Is there a way to use a different IAC?

I could tuck an isv valve away under the IM for use during winters and delete during warmer weather. Two different maps. Maybe make a plugnplay pig tail to run from the stock harness TB connector and split it to two legs, TPS for the TB and then a two wire connector down to the ISV.


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Just a case of deleting the pigtail and deleting the lines to the isv come winter.
Why do they stop at 250 hz, is there any board modification or future changes to go higher freq??


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So the TPS and the iac valve are all the one.......and .....Well I feel like a fool for not seeing it or trying it sooner......but, I noticed the 'iac on' tab going green, on and off, as the rpm was hunting up and down. So the idle was getting switched off with TPS !! The iac motor would open the valve(throttle plate), in turn the TPS %(&rpm) would increase with it, reach the threshold of 1% and switch the iac control would drop off > valve closes bringing TPS below 1%, idle control would enable again below this 1% and it would keep cycling like that ......revving the engine.

so, I raised the 'TPS threshold for iac enable' from 1% to 10% to try it out (probably can drop it to Id say 5% later when I have more time to play) and the iac works perfectly with dc curve, it's -2f outside and started and idled fine.
Is there a downside to setting the threshold at around 5%????


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The IAC will just kick in sooner when letting off of the throttle and will keep going when you get back on it until you are past 5%. This may or may not hurt driveability depending on your tune and TPS. Try it out and if you don't notice a problem, keep it!

For now I'm leaving the PID off and just using ign idle control, ......once I'm at 60deg the ref dc is zero so it won't do anything anyway.
It seems to drive fine with the PID control dissabled but ....
Like you said I will see what it drives like when I have the PID set up and the TPS threshold at that setting, hopefully it will behave!!


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Been playing with this thing trying to get it working , but only using the iac dc untill coolant is at 70 deg then dropping it to zero and letting the ign advance do the rest. I tried using PID to control it at all temps but it's horrible, and it's no wonder, the OEM control is a little more complicated lol. Taken from another persons report on testing:
"I scoped the two wires driving the DC-motor in the throttle housing. At steady idle it is stable with a frequency of 500 Hz and a period of about 0,4 ms period. I gave it some throttle and let go. When the ecu senses the rpm going down it inverts the signal to the motor. Then when the idle is stable again it switches back"

So I'm thinking of using a 2wire bosch iac valve as it doesn't seem like VEMS has or will have capabilities to mimic the oem control of this system.

The valve I'm planning on plumbing in is a bosch
0280 140 516
The iac is setup as INJ output 7 , and as pwm. Is that suitable for that type IAC valve??? Do I need to worry about messing anything up or safe enough plug n play and change reference dc values and maybe frequency. It says it uses 1A & 9V fully open.

For anybody wanting to read the full thread http://www.msextra.com/forums/viewtopic.php?f=4&t=38238

Was also considering this as It looks nice and plumbing would be neater. http://www.diyautotune.com/catalog/cust ... -p-69.html
Looks like it's a 4 wire stepper though, bit more wiring and config changing....looks cheaper and easier to get the bosch pwm

Your description of how the valve works when scoped on a stock setup sounds like how it should act with properly tuned PID. Not to sound like a jerk, but I don't think the OEM control is any more complicated than what VEMS is capable of providing. I think you just haven't tuned it properly.

Have you read my guide to tuning PID?

You don't sound like a jerk. I'm not actually the one who scoped it.
The Vems is capable of inverting the signal in that manner??I didn't know this.

When you tune the PID to control the idle nicely, which I managed, it effects the action of the throttle valve. It's not a seperate air valve like I think you are misunderstanding

The iac motor drives the throttle plate, its directly attached.
Do you think 500hz and 250hz will have the same action on the motor, I think not but....? And to have the polarity reversing like that would also effect it too no??

You really would have to experiment yourself to see, as I don't seem to be describing the problem. From lugtronic "The idle switch tells the stock Ecu to maintain steady fuel and timing" when the throttle is fully released. The stock ecu uses the 2nd pot for idle motor position (not the TPS pot) when the idle switch is made....So you can then use the iac motor to open and close the plate and ecu uses dedicated idle control maps, which vems has not got yet.

When the idle switch is then broken the ecu doesn't use the idle map anymore. This along with the horrible action of valve with vems ...... Not good.
Say I'm setting the reference as instructed in first steps of iac control. I give the valve 22% dc. It won't react untill I touch the gas pedal. Then with that assistance it can get to the 1100rpm I'm targeting. This is different to a seperate pwm idle valve like it looks like a lot of people use.

Other people who gave used vems and MS have gone to a seperate 2 wire iac like older models you guys have and it works flawlessly, and before doing so had the exact issues I had, and many of those had a lot of standalone setups under their belt too.

It would be great if the valve response withVEMS was like OEM, then maybe table switch could be used , switching with input from that idle switch in the TB.

I see the vems bridge output driver to control electronic throttle has a max of 8khz

OK I went back and read your posts and now see what you mean when you were saying throttle valve. Sorry, I definitely did misunderstand you and was thinking we were dealing with the single variable of the IAC only.

There is probably a way to control it like stock, but I think you'd be wasting your time. I never saw the need for an IAC at all on my car to be honest. There are rare occasions that they help, but I never used mine 90% of the time. Anyway, as you said a simple IAC would be all you need to get the car running nicely. If you were really determined to do it though, you probably could make an idle map and make a controller to control both the IAC and the throttle plate. It'd probably require a little extra hardware though.

I must be the only guy running a piggyback on an Audi. Why? Its different, it works, if you don't want monster power and all the small difficult shit still works. Mostly. Like AC and idle control. And knock. And cold start...
Stuff like that.

Just FYI, check my sig. Yep, 630cc Dekas and E85 on an AEB. Only 10psi on the K03, but its hilarious. Especially 3rd gear.

The only thing I'm having against the VEMS is lack of control for this stock throttle body iac motor, it would really set Vems apart from ms and others if they got this sorted. Besides that- it's all you could need, with the features and options its apples and oranges to piggy back for me.
So summertime chicago getting muggy and hot.....I got sick of trying to fine tune the stock iac for ac. I'd have it perfect with AC and driving, and then sometimes warming up or driving it would hang and act strange.......
So I had nothing else except a purge valve around and used it to tide me over untill my ISV valve gets here. The pwm purge valve is a little noisey but works a treat in this emergency lol. With it I have nice steady warm up, steady idle ~ 850-900rpm and with ac on ~950rpm and no cutting out at all.
Next install round display and flex fuel sensor I got from Marc at EFIexpress.

Then Injectors,E85 and dyno

Kevin Black at Lugtronic apparently knows how to implement good IAC control on VEMS. However, it is most likely a closely guarded secret.