RPM drop

BRIANTRUSSELL22

MEMBER
2007 CHEVROLET IMPALA
3.5L
V6
4WD
AUTOMATIC
155,000 MILES

I have the car listed above that at 30 MPH or above, even at 25 MPH at times, it will hit the average about 1500 MPH it needs to be at when trying to keep the speed the same then slowly as you apply the pedal more the rpms will go down and you can keep it at 1200 or 1300 or wherever within that 500 MPH drop and the car does not jerk or do anything its just losing rpms then when the pedal is applied far enough the car jumps up to 2000 rpm and will take off normal. Prior it did slip and jerk but it didn't at first then started to and got worse and eventually after a week blew my transmission. I paid 2400 had it completely rebuilt with top of the line parts and new lines and all. Got 30 minutes away from the shop and the MPHs did this dropping thing again but as I said now its with no other symptoms. There is no check engine light and as I said it drops slowly and gradually as you apply the pedal more until its applied enough to jump up to 2000 MPH and take off. I'm stuck between 3 things. MAF, IAC, or the pedal position sensor but I need help and opinions. I paid $3,000.00 for this car a month ago and within 3 week had to pay $2,400.00 for a transmission. This car drives amazing besides the MPH drop and I really need to get this figured out.

Friday, April 30th, 2021 AT 4:52 AM

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

This could be an engine sensor issue but we need to monitor them before we know it could be one of them.

Do you have a scan tool that you can hook up and watch the live data? We need to see the MAF sensor showing proper air intake and then the MAP should drop as you are opening the throttle. I show that this engine has both sensors so if one is faulty then that could cause the issue as the ECM is looking for increased air to deliver more fuel which will raise the RPM.

If the RPM is slowing dropping but the accelerator is increasing then eventually the ECM will think that you are wanting to down shift and so it does. However, it is doing it from a lower RPM then it should so it jerks.

https://www.2carpros.com/articles/mass-air-flow-service

It is most likely not the IAC as this just controls idle speed and is not used at higher RPM or speeds. However, you can clean it as well since this is a new to you and while you are there. Here is a guide that will help:

https://www.2carpros.com/articles/idle-air-control-valve-service

Please let us know these values of these sensors while this issue is happening and at idle and we should be able to determine if they are an issue. Thanks

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Saturday, May 1st, 2021 AT 9:23 AM