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Idle Hunting On Stock Car

Posted: Mon Dec 25, 2017 4:01 pm
by BlackAndChrome
Merry Christmas! Shame today feel like the only day I've had this year to really dig into my car!

I've got a stock 2012 SI with 105k. Previously I had posted about having inconsistent Trim values while trying to tune AFM Flow. Due to being out of town for work it's been a few months since I could even touch the car. I was due for plugs so replaced those and I replaced the upstream O2 sensor at the same time. I cleaned the MAF sensor with MAF cleaner and went back to trying to tune AFM flow this week. I still seemed to be getting inconsistent values and I feel like I've rules out a lot of things but still haven't found the issue. Related or not I also started having problems with idle hunting when warm, returning to stock eq did not resolve but I have remained there for the time being.

For the time being I'm hoping that solving the idle hunting will solve my AFM/Trim issues.

I've heard air in the coolant can cause this, there was air at the top of the rad but a top off and burp hasn't fixed the issue.
I've used an unlit propane torch to look for vacuum leaks but could not locate one (I am no expert at this to be fair, so not entirely ruling this one out)
I pinched off the PCV valve and the issue was not resolved.
Throttle body has a tinge of carbon but nothing that looks bad to me.

The thing that makes me want to discount a vacuum leak is that my trim values (again all stock) can total -25%+ longterm, in the attached log it drops to -15%L and -24%S momentarily, I would think that if I was looking at a vacuum leak the trim values would be positive or at least increasing since before I was having idle issues if this is just an out of spec MAF sensor.

At the same time AFM.v seems to be rock steady related to TPlate.

Hopefully someone has some input. Kind of afraid to drop this car off at the mechanic for equal reason of being stupid simple or really expensive.

Attached log is idle warm up, short drive, and idle hunting.


Re: Idle Hunting On Stock Car

Posted: Tue Dec 26, 2017 8:26 am
by Hondata
The AFM and O2 look ok. I would guess it is the throttle body. You could try disabling the overrun throttle opening parameter, but if you can find a low mileage replacement throttle body I would swap it out.

Re: Idle Hunting On Stock Car

Posted: Tue Dec 26, 2017 6:32 pm
by BlackAndChrome
So I'm trying to fully understand this before I act on it.

I notice that post warm up before initiating an oscillation the TPlate is holding 3-4% where as after warm up and during oscillation the TPlate is 4.5-5%. I have a log from August that shows 2-3% following throttle drop. I also notice that TPlate during driving is not tracking well with TPedal on throttle drop off but I initially dismissed this as this cars characteristic rev hang or now a symptom of the unlearned idle. Was there another clue for you that points toward the TB?

What I'm seeing is that the RPM stabilizes enough to go into closed loop, Fuel Status changes to 2 then promptly 4, FS of 4 and 0% Tpedal means engine brake, cuts the injectors, waits for RPM fall exits closed loop, restarts injectors in open loop and repeats.

Is the thought that the TB is just not restricting air intake enough at idle to not have the RPMs run away? From having someone in the car with ignition on but not running and having them play with the accelerator the TB seems to open and close fully and smoothly. I guess it seems odd that the TPlate is capable of going to lower percentage, and that the AFM tracks well with that percentage, but it looks like it simply doesn't want to go there.

I ran a stock EQ calibration with -5% on AFM flow and overrun throttle opening disabled with no change, log attached for reference. Any other troubleshooting steps I could try?

Re: Idle Hunting On Stock Car

Posted: Wed Jan 10, 2018 11:13 am
by BlackAndChrome
For anyone that references this thread in the future.

I replaced the throttle body and the issue persisted, so I dropped it off at the dealer. $150 later they relearned the idle and apparently it runs fine. $150 for something I should have done in my driveway but lesson learned.

Not sure if an idle relearn would have resolved the issue with the original throttle body but it would have been smart to try ( and even smarter to do after the new TB). Not sure why it lost the learned idle to begin with though, I had not touched the TB before the issue arose. My only thought was the MAF sensor cleaning but I didn't think that was significant for idle.

Re: Idle Hunting On Stock Car

Posted: Sun Feb 25, 2018 2:17 am
by Johnny42142
I’m have the exact same issue. I was previously on the CAI intake
ca back exhaust base map and flashed my car back to stock and started having the idle surges. Just curious to know if you took your car to the dealer on any base maps and if you had any mods at the time. Thank you