Temperature related idle surge
 

I'm trying to work out an idle surge issue that is bugging the crap out of me! Maybe someone can point me in the right direction.

As soon as my temperature hits 89C (192F) the idle will start to surge from 1k to 1.8k , and will not stop unless the temp goes back down to 88C (190F).... Every time, very annoying!

It has been happening ever since the fresh build...Power FC, simplified sequential.

Feels like a logic issue controlling the idle air control valve...this happens with the IAC plugged in or disconnected, but disconnected seems to be way more erratic.

Has anyone come across this problem, need some direction here. Since it happens at exactly 89C every time it doesn't seem to be mechanical, do I need to set up parameters in my power FC different?

Video
 

Here is the video of the surge...

Because it seems so exact in relation to temp I'd start with the coolant sensor.

Im keen to know the answer to this,, i have exact same problem.
I scratch my head what changes at 90degrees to cause the idle to bounce

I'm curious too.

As mentioned I can't imagine anything but a water temp sensor being that accurate in relation to sending a signal to the ECU to effect idle that dramatically at that exact temp.

I don't have a manual at my desk and can't remember what the thermosensor even does but my 1st thought is it reduces idle once the the coolant reaches a certain temp. So if it's freaking out it may be on and off causing the surge.

However for all I know the PFC doesn't even read it and it has no control over idle at all :)

Anyway good luck :icon_tup:

What temp are the fans set to come on? With the PFC if you are still using the ISC and ignition controlled idle the PFC will bump the idle up when it sees an electrical load (Fans). It is probably surging because the PFC is trying to bump up the idle and you have different ariflow from before your latest build. You need to check for vacuum leaks, confirm the TPS is in spec, adjust the idle at the throttle body, then perform the powerFC idle learn procedure.

Did you remove the 4 wires from the ECU connector as instructed in the Dale Clark PFC manual?

I'm willing to bet that they're still connected. My old FD did the exact same thing until I removed those wires.

Bingo that could be it :nod:

Thanks so much for the help guys! Funkspectrum I will remove the 4 wires this weekend and let you all know how it goes. I cant wait to solve this issue! Hope you all have a great week!

My trailing and leading ignition wires were swapped when that happened to me.

Yeah. It'll take you 5 minutes if you wanna just clip the wires from the harness itself. Just make sure to wrap the exposed parts with electric tape or something so they don't make contact for any reason.

did your car do the surge before you installed the pfc? have you driven the car while its doing the surge? does the throttle seem a little off while its over 89C? does it surge when you have it in 1st gear at and idle forward, bouncing between the same rpms?

Naked n fearless-

No my car did not surge before the power FC

Yes, I have driven the car while it surges...yes, super annoying!

Yes it does surge in all gears over 89C, and it does bounce between the same RPMs.

Im looking forward to cutting those wires over the weekend to see if it takes care of this issue, thanks again everyone!

I have attached the Dale Clark PFC manual for anyone to review if needed, page 10 shows the wire removal procedure.

I'd recommend removing the pins on the PFC versus cutting up your harness if you're comfortable doing. I work at a veterinary hospital so it's super easy to do with hemostats.

Hey guys, just want to give you some great news!!!! I cut the 4 wires at the ecu today per Dale Clark PFC manual and the idle surge is fixed! Ahhhh, feels soooo good! It also fixed another issue i was having with boost, after hard accel boost would cut out for about 15 sec...not anymore! Thanks for all the help on this one guys, dont know what I would do without you!