Hey all, I'm new here and have a very odd issue with my 2018 Mazda 3 (56,000 mi). The Senior mechanic at the Mazda dealership mentioned that he has never seen anything like this before and I'd like to see if anyone here may know what is going on because I really don't want to have to dish out a bunch of money testing out what could be wrong.

The issue:
When accelerating in cold ambient temperatures the vehicle's acceleration sporadically disengages. This can happen a few times during a 20 minute drive and speed does not play a factor. I tested in both normal and speed modes and it happens in both. The only way to re-engage the acceleration is to release foot from accelerator and press down again. The concern is when entering a highway or changing lanes where every second counts when expecting the car to accelerate.

This issue only became a problem after I serviced my vehicle at a Mazda service center. In winter 2022 I brought my car to the Mazda service center for an oil, brake flush, and front brake change. They recommended me to replace my engine and cabin air filters as well since the mechanic mentioned that they were very dirty, which I agreed to replace. The following week the car began to have this sporadic acceleration loss issue and I quickly returned it to Mazda. I explained that I did not have this issue before bringing it to them and they told me that I couldn't prove that and didn't believe me that I had this issue. After speaking to their senior mechanic, he asked to test drive my vehicle, which I accepted and the issue happened to him. He was shocked to see the issue since there was no warning messages. He mentioned that it could be the mass airflow sensor having a particle from replacing the dirty engine filter, but wasn't convinced since that should return a warning message. He then thought it could be an issue with the throttle bottle getting stuck closed. He offered to briefly clean my throttle body for free, which he did and took 2 minutes doing so. The issue seemed to go away, but did occur once more a week after that. This was also when the weather was starting to warm up again into spring.

Did not have this issue all spring, summer and fall until temperatures starting dropping below 40*F. So I am convinced that the cold temperatures if affecting this issue. I did have to replace my spark plugs and ignition coils at approx. 54,000 miles which seemed early since their life expectancy is about 75,000. This could have been related, but was fixed in the summer. There was no acceleration loss during that time, just the normal misfiring from a bad ignition coil. I always let my car heat up in the morning too, and the car operates perfectly except this issue.

My questions:
How could a throttle body get stuck when it's supposed to be open when the accelerator is pressed? I personally don't think this is an issue with the throttle body, but a sensor/computer issue that is telling the throttle body to shut when it shouldn't.

Would a faulty mass airflow sensor cause this issue without showing an error message? PV=NRT. I know that in colder temperatures airflow is decreased.

Are there any other sensors that would be affected by cold temperatures or would cut the acceleration?

Is there something I may be missing? I am mostly looking at the airflow side, could there be an issue with gas delivery to combustion chamber in cold temperatures?

TLDR: Acceleration loss happens sporadically in colder temperatures. The only way to re-engage is to release and re-engage the accelerator. Please help.

I appreciate any feedback and discussion.

 

Going to buy MAF sensor cleaner and try that.

Today was a cold one. Car lost acceleration power multiple times for a less than 3 mile drive.

Oddly enough I noticed that the RPM on the dash screen did not decrease when the acceleration was lost. However, the engine did not sound like it was running at that RPM.

Now I'm more curious. Could it be a de-clutching issue?

 

This is a fascinating issue indeed! I don't have any earth-shattering suggestions.... but it is very strange that the RPMs don't change on the tach but the sound and power decrease. I did note that you said he only took 2 minutes to clean a throttle body.... that seems pretty fast to have been done properly/thoroughly. Since this started after filter changes, I would normally suggest that they forgot to connect/fully connect something but if that were the case it would be throwing a code. Interesting indeed! Hopefully you find the fix! Let us know if the MAFS cleaner helps.

 

What you are describing should have generated a DTC(s). I would have another look at the ECU for DTC pending and active as well see what the monitors look like.

DO NOT replace any parts until you confirm they are at fault.

Be careful cleaning your MAP and while you are them don't forget to pull and clean your IAT sensor.

Somewhere on my thread you can see servicing both of these properly.
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While not absolute but a thought ...there is no mention of the drive-by-pedal assembly being tested? But then again if it were starting to fail there would be a DTC relating to that.
The service you had done, and the subsequent issues are only a coincidence I would not think too much about their relationship between that service and your current problems. Yet!

 

Just curious about your username can I ask what it means?
BTW everything you posted is good info, but I should add would have also generated a DTC and the monitors would be in fault or not readiness state.

The throttle body properly cleaned need to be removed from the intake system off the engine.

 

Update:

Got a good code reader for Christmas. Did some tests and it looks like I am getting P2299:00 code when the issue occurs.

I am no longer thinking that this is a MAF sensor or Throttle Body issue. I believe that a faulty brake sensor is telling the PCM that I am braking when I am not, which is disengaging the throttle. According to P2299:00, a check engine light would not be thrown unless the issue persisted over 5 seconds, which it is not. However it is happening long enough to tell the PCM to go into failure mode and then back to normal operation mode after I re-engage the accelerator pedal.

This could make sense considering that the Mazda Technicians replaced my front brakes and brake pads and did a brake flush. Perhaps they pinched a cable, or did not properly calibrate the sensor with the new pads? Odd that this issue only persisted when it cold.

I am doing some more diagnostics to see if this is the sensor at the wheel or by my brake pedal.

Any information regarding what type of sensors are at the wheel? Is it just the ABS brake sensor?

 

Any ideas what could be causing this?

The car seems to be thinking it is braking when it is not. Would a sensor by the wheel cause this?

 

That problem should still be covered under WARRANTY? You need to return to MAZDA asap because it may be affecting the braking system and other safety and stability control systems.

 

These were the DTCs that were shown:
C0040:23-08 Brake Pedal Switch A
P0504:00-28. Brake Switch A/B Correlation
P2299:00-2C. Brake Pedal Position/Accelerator Pedal Position Incompatible

There is no braking issues when pressing the brake pedal. The PCM seems to be receiving information that the brake is being applied when it is not. My brake lights do NOT illuminate when this issue happens.

My floor mat is not an issue, it is Mazda standard and I even took it out to test it. I am not pretty both the accelerator and brake at the same time.

Based on these conditions, is it possible to narrow down which sensor would be the issue?

It's odd that this issue only occurs during the cold. Perhaps the connection to the PCM is loose?

 

There is no guessing.. sorry. Each code needs a specific diagnosis checking to rule out. I strongly suggest not to randomly remove any sensor as it could void your warranty.
If you are going to check your ECU then I recommend disconnecting the batter negative ground first. If you break the ECU connector lock on the harness it will void several warranties associated with your Mazda.