Bosch idle air valve question

bertelli_1 · Post by **bertelli_1** » Sun Apr 16, 2006 1:15 pm

I'm running a V3 board on my VW Golf and want to use the idle control valve do to a poor cold idle speed. from what I've

I need to upgrade the transistor in Q4 and remove a couple of other components. Is this the best way to use the valve of is there another (simpler) way??

keithmac · Post by **keithmac** » Sun Apr 16, 2006 1:39 pm

On my 2.2 boars the only modification I made was to replace the FIDLE transistor to a TIP122, ran the fidle wire to the -ve of the Bosch PWM valve and +12v to the other side of the valve.

FixItAgainTony · Post by **FixItAgainTony** » Sun Apr 16, 2006 2:22 pm

Opps - quick edit... The only way to do it to change the componets you have read about. It is a little easier on the V2.2 board because it has the type of flyback protection needed and does not have the current protection circuit. You can implement the V2.2 circuit on the V3 board by upgrading Q4 ...

You will have to replace the transistor with something that has a higher current rating. A TIP 120/121/122 Darlington works well. Note that if you use a TIP, you need to insulate the case / thermal tab - it is connected to the collector of the TIP.

I have idle air control running on the bench - just have not bothered to put it into the car. I used the 2 wire VDO solenoid valve (408.202.008.001) from a BMW. Replaced Q4 with a TIP122 and R39 with a remotely mounted 0.3 ohm 10W resistor (what I had available - this allowed me to retain to retain the current limiting feature of the circuit. If you do not want the current limit feature, you can put a jumper in place of R39. Q20 becomes non functional, leave it or remove it - your choice)

I mounted the TIP122 where Q16 (VB921 coil driver - I do not use this). Just solder in some wires from EBC of Q4 to the corresponding points for the TIP. You can use unpopulated IgbtOut, R43 and R57 to provide a place to solder the wires for the TIP EBC. If you are using Q16, just mount the TIP to a heat sink someplace and connect to the Q4 EBC points.

Again, note that the case of the TIP is connected to the Collector (C) so it must be insulated from the heat sink.

Also, the zener diode D8 will not handle the flyback from the solenoid. Not a question of if it will die, but when. It will die. Others have seen this happen. You will need to review the V2.2 idle air circuit and implement that for flyback protection. I did this by adding a 2W diode from the solder point on the underside of the board by the "B" of the IAC1B silk screen (the collector of the TIP the way I have it wired) to the Anode of the diode and connected the Cathode (banded end) of the diode to the MOV 12v connection. Do a search, I think other people have posted similar solutions.

Measurements on the valve indicated max current to open is ~1.35Amp at 13.5V. MegaTune % closed = 90% starts to open. 30% valve is completely open and no longer buzzing.
Dead short on output => 2.1A.

I have also used this set up to drive the idle air control valve on a Subaru throttle body. It seems to work well.

There have been reports of the PWM idle control causing noise problems. You may want to ground the collector of the TIP in a solid location. Connect the Cathode of the flyback diode to a solid 12V line.

Good luck,
Charles.

bertelli_1 · Post by **bertelli_1** » Mon Apr 17, 2006 1:41 am

Thanks guys. By the way KeithMac - what happened to the ClubGti forum??

keithmac · Post by **keithmac** » Mon Apr 17, 2006 1:50 am

http://www.clubgti.com/forum/index.php

They`ve re-done the whole forum, the .co.uk doesn`t work at the moment. You can still use your old username, check your SPAM folder in e-mail if you didn`t get an e-mail from them (I`m on AOL and it went straight ti SPAM

).

hobieboy · Post by **hobieboy** » Wed Apr 19, 2006 10:15 am

As an alternative, can I simply use the existing transister on the V3 board to drive a relay; which in turn drives the actual PWM valve?

thanks.

keithmac · Post by **keithmac** » Wed Apr 19, 2006 11:25 am

Doubt it, due to the speed at which it would need to switch a normal mechanical relay wouldn`t be up to the job.

You could possibly make an add on box with a tip122 etc inside and drive that from the fidle pin if you don`t fancy replacing the MS transistor but it seems a long way round..

hobieboy · Post by **hobieboy** » Wed Apr 19, 2006 5:13 pm

Thanks for the explanation. Guess I'll change the transister inside the MS box then. Not a big deal but since I'm already making an add on box for the ignition drivers thought I can house the relay there too but was worried about speed as well.