Hunting idle, Pretty sure its the head temp sendor Options

[VaccaRabite]

Caveat: I'm using custom fuel injection (Microsquirt)

So this weekend my idle started hunting. I was pretty sure I had sprung a leak somewhere that was opening and closing a miniscule amount while the car vibrated at idle.

My idle would go from 1000 RPM (where I have it set) to about 1900 RPM for a few seconds and then settle back down again. Whatever, drove the car for 300 miles anyway. Only time when it became an issue was at stop lights and trying to get through the free bridge traffic jam between NJ and PA - and then it was just an added annoyance.

When I got home I did not find anything obviously wrong. I plugged my laptop in to see if my IAC had gone out of compliance. It was fine but I noted my "coolant" temps were all over the place.

Coolant sensor for me is the stock location head temp sensor, plugged into my ECU.

Are these things known for failing? Mine was giving readings with a 100+ degree swings every few seconds (I'm guessing cutting out), and my idle air valve was opening and closing trying to keep up, hence the idle hunting.

Zach

[GregAmy]

You're not gonna like this but...

There's only a handful of us running MS systems, and each one is bespoke. For one simple example, we have no idea what CHT you're using, so asking on this board "are the CHTs subject to failure" is pointless (or it gets you responses from guys who think you're running the stock CHT sensor, which actually won't work on MS unless you have some kind of pull-up resistor circuit on it). We don't know what you have, so we have no idea if that is subject to common failure.

For another example, I'm not running an idle air valve controller with my self-designed Microsquirt system (quite successfully, I might add) so I have no idea what you're using or how you have it set up or are controlling it.

I personally spent a lot of brain time thinking through and building my design and I know it well, but I don't know yours. And I can't spend time learning your design so I can guess over the Internet if your CHT is the problem.

Further, probably none of us here is qualified to review your Megasquirt logs and see if maybe something is borked.

Did you buy this as a bolt-on system from someone (DubShop?) You can ask for help there.

Nope, we treaded off the beaten path with Mega/Micro. Lack of support from OE boards - or limited support from the aftermarket boards - is what we have to accept on these systems. Maybe that'll change over time if more 914 owners install these systems?

So I strongly encourage you to hit the Megasquirt support forums. Those are the MicroMega brainpowers, and the primary support system for these DIY EFIs. I've been there often (sometimes daily, reviewing posts) and have gotten decent support.

GA

Edit: If you are running the stock sensor in the stock location, switch over to one of these: https://thedubshop.com/modified-coolant-temp-sensor-package/

Alternatively, switch to a K thermocoupler under the #3 spark plug - much more useful information for engine safety - and port it through this device: https://www.adafruit.com/product/1778