9thgenidiot

2012 Civic LX, 192k miles.

I've been having symptoms of a vacuum leak in my 2012 Civic and am wondering if my coolant temp sensor is bad? Symptoms are surging on acceleration (does not happen always), high RPM idle on cold starts (sits around 900-960 for a solid 10mins), very slight RPM bouncing on cold starts (1,000 to 1,100 and back), RPMs bouncing up whenever RPMs drop to ~1k while decelerating, loss of power while accelerating.. also a very faint whistle noise that isn't constant, and seems to go away when I take my foot off the gas.

I've checked for vacuum leaks but can't see or hear anything, and fuel trims are normal (-3 to +3 %). No CEL, no codes stored.

Here are some readings of my coolant temp sensor from my OBD2 scanner-- ALL were taken during cold starts after the car was sitting for at least 6-8 hours.

Actual Readings vs. Ambient (outside) Temperatures:

Reading: 122 degrees F
Ambient: 66 degrees F

Reading: 80.6 degrees F
Ambient: 73 degrees F

Reading: 77 degrees F
Ambient: 62 degrees F

Reading: 104 degrees F
Ambient: 85 degrees F

Reading: 80.6 degrees F
Ambient: 67 degrees F

Reading: 78.8 degrees F
Ambient: 75 degrees F

Reading: 100.4 degrees F
Ambient: 83 degrees F

Reading: 80.6 degrees F
Ambient: 75 degrees F

Reading: 118.4 degrees F
Ambient: 70 degrees F

Reading: 86 degrees F
Ambient: 76 degrees F

Reading: 86 degrees F
Ambient: 79 degrees F

Reading: 80.6 degrees F
Ambient: 75 degrees F

Reading: 80.6 degrees F
Ambient: 73 degrees F

Reading: 84.2 degrees F
Ambient: 69 degrees F

Reading: 82.4 degrees F
Ambient: 80 degrees F

Reading: 96.8 degrees F
Ambient: 88 degrees F

Reading: 109.4 degrees F
Ambient: 80 degrees F

Reading: 90 degrees F
Ambient: 61 degrees F

As you can see from the red entries, the reading is often well over 10 degrees difference on cold starts.. sometimes 30+ degrees of difference.

Is this normal? My car is not garaged but I don't know how much that can affect it, if at all.

Thanks

DCFIVER

Yup,normal.
The temp sensor does not have nearly as much authority over fueling events as it did in days past. OBD 2 PCMs are rational type and would pick up on and code for ECT faults.


I suggest cleaning the throttle body for starters(In lieu of any actual testing,which I cannot do from here)

holmesnmanny

The high idle on cold starts is completely normal. It's designed to warm the car up faster. If your car is an automatic, it's likely the rpm bouncing is simply your car shifting.

It's possible your spark plugs might need replacing. You could check your air filter for cloggedness as welll.

9thgenidiot

Thanks @DCFIVER and @holmesnmanny.

The throttle body was actually cleaned out around 175k miles or so, but these problems were happening before that and continue to happen now. The thing is, I don't remember the RPM bounce happening until I had my TB cleaned.. I did have even worse hesitation prior to cleaning the TB, so cleaning it definitely helped with a lot of my problems, but there is still something causing additional bucking and sluggishness on acceleration (along with the other issues I mentioned).. very frustrating!

I put in new OEM Denso plugs at 150k (42k miles ago), so I'd be surprised if it were the plugs, but who knows? Maybe they aren't torqued properly? I'll check them and probably swap out for NGK either now or at 200k miles so I'll let you know if that resolves anything.

Air filter was replaced. I'm thinking the RPM bouncing is a symptom of an issue rather than a transmission-related thing since it happens even when in Park. If I give it a little gas, the RPMs go up but then bounce on the way down RIGHT when they hit 1,000... it just bounces up to 1,200 or 1,300 one time, then back down again to the standard idle RPM. Very weird. Any ideas otherwise? Again I don't really remember having the RPM bounce issue until my TB was cleaned. Could the throttle body / plate be damaged causing issues? I wonder if the mechanic stripped a gear or something and now the throttle plate is messed up / re-opening, causing the RPM bounce?

Thanks again!

DCFIVER

Yes,entirely possible,especially if does not know how to clean an electronic TB. Ive seen it happen on more than a few occasions.


Youre gonna need an enhanced scan tool to look at relevant data PIDS(APP 1& 2 and TPS 1 & 2)

holmesnmanny

Can you make a real clear video for us to see what is happening ? Make sure it's clear, sometimes people post vids on here and you can't see sht. Just use common sense, if you can't see it, neither can we.

9thgenidiot

Ok thanks! I do have a Bluetooth OBDII scanner with Torque Pro that has access to monitor the TPS and APP. From the monitors menu I see "Absolute Throttle Position", "Relative Throttle Position", along with options to monitor Accelerator Pedal Position. Are there specific numbers I should be looking for (i.e. should both the TPS and APP have the same value, or should they be changing at the same rate?).

I did try putting my key to the ON position (not starting the car), graphing the TPS and slowly pressing / releasing the gas. The graph line seemed consistent and didn't contain any spikes or drop-off points, indicating to me it was pretty responsive to what I was doing to the pedal. But I'm sure this isn't a proper way to fully test it but at least showed it was responding to the pedal.

Sure I will record it today. The RPM spike portion is hard to explain. I'll make sure to get it clear and explain when my foot is on/off the pedal so people can see exactly what is going on. Should have it up by later tonight or tomorrow