Idle issues after coolant reroute!
 

Last night I swapped my old nasty radiator for a KoyoRad with Mishimoto fan kit and put a coolant reroute that I picked up off another user here on the forum. The reroute is supposedly an older 949 style reroute, which it could be but I’m not 100% sure. It uses an adapter plate that I haven’t seen anywhere online, most the newer reroute are one piece instead of 2.

So now that everything is installed the car idles at about 2k rpm after it runs for a few minutes. On cold start instead of the idle dropping after a few minutes it goes up. With the car at operating temp the idle bounces between 2k and 1k rpm pretty rapidly. I’m not sure what to make of this, I checked all my connections, gonna check for vacuum leaks and that’s really all I can think of unless y’all have any other ideas.

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Another observation, at idle car is at 2k rpm. If I place my foot on the brake pedal is when it immediately starts to bounce. I’m assuming vacuum leak or IACV

Disconnect and plug your vacuum booster hose. See if it alters the problem...

Coolant sensor not grounded? Assuming all else is as it was prior to the install, this is the only electrical item you altered.

Do you know where the coolant sensor grounds to? I did have to extend that harness about 6” or so to reach the new spot and I wonder if maybe that wiring isn’t up to par, although I did solder it and it was solid. Maybe I used the wrong wire or something.

I wasn’t aware the coolant sensor had any relation to idle speed. The fans kick on at the appropriate time as well which kinda moved me away from that sensor

I've read it grounds to the block...others have had issues in the past with spacer-type reroutes and temp sensors not grounding. Nothing I have personally experienced (I had a Supermiata reroute in the past).

Should be easy to jump the ground from the sensor body to the block to see if it's an issue.

So the car literally just randomly stopped doing it last night after 2 solid days of a screwy idle. I drove home from my buddys house and after 30 min of driving, as I pulled into my driveway the idle went down to 900 and hasn’t done it since