PWM IAC Transistor Install

[SBF Fiero]

In the Megamanual for install of the PWM IAC valve it says the following:

For PWM Idle Valve Users Only
Note - if you are using a PWM idle valve (Ford or Bosch 2 wire valve - see this link for more information), these valves can not be operated with a relay. As a result, they need a higher capacity transistor installed.

DO NOT install Q4 for use with PWM idle valves - it cannot handle the current directly for PWM idle valves. ('On/Off' type idle valves used with a relay are fine with the default Q4.)

Instead, for a PWM idle valve, use a TIP120/121/122 transistor (such as Digi-Key 497-2539-5-ND, 74¢ ea.) mounted on either the heat sink (if you have a spare spot) or the case. You should use a mica insulator (4724K-ND, 93¢) with heat sink grease as well. Run wires to the Q4 connections as shown below:

Now I understand what it is saying, and I have the correct transistor and the diode and the mica insulator and the heat sink grease. Now my problem is that part where it says:

mounted on either the heat sink (if you have a spare spot) or the case.

I do not have a spot on the Heat Sink, and I'm not exactly sure how to go about mounting it on the case? I apologize if this sounds like a Stupid question, but I'm just not getting it.

I searched through this forum and was not really able to find the answer.

Thank you in advance for the help!

- Jeff

[DonTZ125]

You're basically talking about drilling a suitable hole in the case for the bolt, and installing it in the same way you installed the various items on the heat sink bar. One thing to be very aware of - you MUST deburr the hole, or else the nylon collar and / or the mica insulator will likely be knocked askew, shorting out the transistor. Either use a 45deg counter-sink drill, or a normal drill that's much bigger than the one used to poke the actual hole. Just touch it down to remove the jagged bits, don't try to go too deep. Make the flying wires long enough to remove the lid easily, and use heat-shrink to cover any bare bits that might try to wiggle about.

[SBF Fiero]

You're basically talking about drilling a suitable hole in the case for the bolt, and installing it in the same way you installed the various items on the heat sink bar. One thing to be very aware of - you MUST deburr the hole, or else the nylon collar and / or the mica insulator will likely be knocked askew, shorting out the transistor. Either use a 45deg counter-sink drill, or a normal drill that's much bigger than the one used to poke the actual hole. Just touch it down to remove the jagged bits, don't try to go too deep. Make the flying wires long enough to remove the lid easily, and use heat-shrink to cover any bare bits that might try to wiggle about.

Thanks! I just installed, now I just need to test it.