Surging/stalling when accelerating. intermittent issue
 

Hey everyone, first post hoping for some help. Have an issue that's been effecting me for a while and the dealership hasn't been any help.


Last summer I noticed that on occasion when pulling out of a stoplight/stopsign my car would accelerate normally for a few seconds then seemingly stall then start going again then seemingly stalls again then go again... does this for about 10-15 seconds or so then everything is fine and drives like nothing happened. No error codes or lights before, during or after, and I don't have to pull off and restart the car or anything.



Car is completely stock except for the air filter. 2015 FRS automatic trans, 125,000 miles. No codes and the car runs fine apart from this happening at random. I bought a little OBDII reader to log and attached some numbers. In the file, if it attached properly, I got two similar instances, one where I accelerated from a stop with no problem then another a few minutes later when it stalled. 188 second mark is the good one, 294 sec is the issue. You can see the RPMs go up normally then they just start going down.


Dealership couldn't reproduce, and everything they checked was fine... at least they didn't charge me for any of the tests they did.

You said: "accelerate normally for a few seconds then seemingly stall then start going again then seemingly stalls again then go again"

Stall is a very specific term which means the engine dies. However, the way you wrote that, it sounds more like what I would say is "bog down", or "sputter".

When the vehicle "seemingly stalls", does the engine RPM drop to zero or near zero, then suddenly restart, or do the RPMs drop well below normal, and then stabilize?

With the logs I have, RPMs dropped from 2800 to 1200 in 3 seconds while accelerating. Then RPMs start going back up and then fall again about the same amount. while the rpms are falling the pedal has no response; I can push it all the way down with the car only coasting forward.



Saying it stalled was more because I couldn't think of another way to describe it.

I'm just trying to clarify what's happening so I can be the most helpful.

I wasn't able to make anything out of the logs. It's just a large number of boxes with numbers in them when I tried to see them. I can't see what's what.

When you have this issue, is the engine usually cold, hot, or does it not seem to make a difference?

Happened at all temps

Wouldn't let me post the csv file of the logs so I converted to pdf. Takes a while to load for me but the columns left to right: Time in seconds, RPM, intake manifold absolute pressure, Mass airflow rate, short term fuel trim, long term fuel trim.

Upload it to https://datazap.me/ so it'll be easier for people to read :thumbup:

Hope this helps

https://datazap.me/u/scarysquash/log...&data=1&hg=2-4

My first thought is that this is throttle body related.

With these cars, accelerator pedal input is a request for throttle angle. If you aren't getting a response when you hit the gas pedal, it's cause the ECU doesn't even know what's going on, or it's in some kind of limp mode.

Usually, with limp modes you stay in limp mode until, at the earliest, you turn the key to off and then back on again. This doesn't sound like your symptom.

The intermittent nature of your issue make me think it's likely not just a dirty throttle body, but cleaning it might be a good idea just to rule it out as the cause of your issue.

The other potential I'm thinking could be happening is your throttle body has an internal mechanical failure that is just starting to manifest. An internal problem would not register a code until it's failing past whatever calibrated failure points these ECUs care about.

If you have the data to compare, I would look to see if you have something along the lines of "throttle angle desired" and "throttle angle actual". If you have these bits of data to analyze and they are not fairly close to each other, that could indicate an issue.

Of course, this is just off the top of my head. There could be many avenues of determining the fault as well as potential failure points.

After throttle body, I would take a close look at the data for the Mass Air Flow sensor, Engine Coolant Temperature sensor, and Intake Air Temperature sensor. If one of these sensors intermittently sends bad data your ECU will be making bad decisions.

Hi ya, scarysquash and welcome to our forum - :clap:

Obviously, there is some dirt in the sediment bowl of the carburetor and it's periodically blocking the jet(s). Oh wait, this isn't 1950 anymore is it? - :bonk:

Since your car is an AT, is there any correlation between when the car acts up and the transmission shifting?


humfrz

It does seem to occur during a gear change. Elsewhere I described it as not engaging the next gear. The first time I brought the car in I had the dealership change the trans fluid and thought they inspected it as well. I know at some point I asked them to look into the shift solenoid.

I'm about due for an oil change. I'll ask the dealership to look into some of these.

You might consider asking the dealership to flash/update the AT computer thing - :iono:


humfrz

Late update...


Been a while but I took it to a new dealership and told them to specifically inspect transmission solenoid and throttle body. They didn't mention anything about the transmission but did recommend cleaning the throttle body as it was dirty. I would be so relieved if the cleaning fixes my issue...not holding my breath though