RPMs drop at red light

[Ghost3366]

Hello ,

I am wondering if anyone has experienced this symptom also. Since buying the car I have noticed at a red light the RPMs will drop a little , shake a little and then return to normal, it happens very fast. This has not happened that often but I would say in the last 8 months of ownership 6 or so times. I just recently added a tune state 1 OTS Cobb, but this issue happened before and after. Looking to see if other have experienced this also.

Thank you

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[5.0yote]

Is this an auto or manual? It may just be a delay of the electronic throttle closing at stop.

 

[Ghost3366]

I have an automatic, it does not seem to follow any pattern in relation to when it happens, weather the car is been driving for 5 mins or 25 mins. It happen twice today right after each other after filling up with gas. Gave it some gas getting onto the street and then came to a red light. Idled fine, and then dropped a little, shakes a little and then normal and then repeat one more time, but then after that at the next stop and others after that one, nothing.

 

[Billy1]

 

[Cheo]

I had this issue, didn't always happen but it did at idle several times. Have not seen it since I replaced my lowside fuel pressure sensor, not saying it's related.

 

[McJ]

I think Billy1 is correct, I had the same issue. I would put my car in neutral (manual transmission) and the revs would drop and car would shake then come back up. Eventually I got an engine code for the evap purge valve.

Then it got so bad my engine would stall because the revs would just fall to 0. Once I replaced my purge valve the issue went away and I now longer have the stall or low rev issue.

 

[Ghost3366]

Thank you for the replies. When the weather gets warmer I will check the evap purge valve. Maybe mine it starting to go because it does not happen that often or as bad as the person in the video explains. Any other suggestions would be great.

 

[3oostdmstng]

Thank you for the replies. When the weather gets warmer I will check the evap purge valve. Maybe mine it starting to go because it does not happen that often or as bad as the person in the video explains. Any other suggestions would be great.

Just my input, I had my evap purge valve replaced under warranty ( inexpensive, anyway), after reporting rpm drops after fueling up and also some random rpm drops at a stop... started at around 43k miles.

I also replaced spark plugs myself.

My problem came back and CEL light came on at around 52k miles...took it to the dealer reported bad oxygen sensor, they replaced the injectors (under powertrain warranty).

Car is behaving SO amazing after new injectors....the car feels "healthier".

It puzzling still because since I bought it, pre-owned with 10k miles only, Ive only used 93 octane...now I have 55k miles...

Im stock with only MBRP catback.

 

[Rick B]

What brand of fuel were you using?

 

[3oostdmstng]

What brand of fuel were you using?

I forgot to include that. Puzzling because I've always made sure to pump top tier and 93 octane, I pump mainly at Shell and BP.
Now, since I bought it CPO with 10k, I have NO idea what the previous owner pumped. It was not a rental car.

 

[Ghost3366]

Thank you for the additional ideas. Then injectors are an interesting thought, which could be true since my car started as a rental , so I can imagine all the cheap gas it saw. Not sure yet how I feel about bringing it in without a code and having the tune. I have to try the other options first then maybe go to that one. Thanks again

 

[bluefirestarter]

My 2015 did the same thing drove me bonkers! I changed the evap purge valve and it runs like a champ now.

 

[ryant601]

Do you have a CAI? Sometimes if the connections aren't 100%, stumbling is a symptom.

 

[3oostdmstng]

Thank you for the additional ideas. Then injectors are an interesting thought, which could be true since my car started as a rental , so I can imagine all the cheap gas it saw. Not sure yet how I feel about bringing it in without a code and having the tune. I have to try the other options first then maybe go to that one. Thanks again

Unfortunately, dealers work with that CEL.
When I had my purge valve replaced, I was the one who mentioned it. I told them that I did some research and that some people mentioned changing it, so they did it lol. You can either take it to them (they should do it FOC as they did for me), or change it yourself as the part is not expensive. When they changed mine, the car did not give any post fueling/rpm drop issues for about 10k miles. I put miles quite a bit (about 1500mi/mo). It did, however, had a bit of a rough idle upon cold starts only, and that is what made me change the spark plugs (which btw looked good), but it helped a bit.

Fast forward a few miles and my CEL light came on (first time since owning the car), just a few miles before the light came on I noticed the car was not accelerating that well. Immediately took it to the dealer, they kept it for about 3 days doing some testing. They ended up changing the injectors.

So far so good. Oh and that rough idle upon cold start is 100% gone.

Good luck.

 

[Rick B]

OP. Any results yet on what the issue was?

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