Unexplained RPM/power loss and dropping revs (posted video of problem)

[johnoski]

First off, I am not a "Car Guy". I know some, enough to be dangerous to myself, but not a great deal.

Background: I purchased my 2009 Chevy Aveo 5 Hatchback from an auto trading dealer back in June/July 2013. The Tire pressure light was on when I bought it. The next day, after filling up the tires, light did not go out. Also, the CEL came on. I took it back to the dealer, and they eventually (4 month's later) fixed the tire sensors and replaced both Cat's for free. Problem solved... So I thought.

Issue: Starting in November when I cooled down, the engine started to randomly loose RPM's and all acceleration while at cruising speeds. This randomness has progressed to everyday, every time, but not all of the time. Sometimes it is within the first 1-5 miles of my 15 mile ride to work, sometimes it is in the middle, and sometimes at the end. It only lasts for about 5 or so miles before it runs normally. It has had the issue at first, worked fine, then 2 miles from destination, started happening again. I can't seem to figure out a pattern. It has become dangerous to even operate the car. I pulled though an intersection the other day and it gave out then. It almost caused an accident. It is very frustrating.

What I have done: I have spent many hours on the internet researching many forums. I have read many post on this forum with not clear path ahead. I changed the spark plugs, I have called the GM dealer to verify the Plug recall had been done (it has), I have checked for vacuum leaks. Again, I am not a car guy so I check by spraying carb cleaner around in the engine compartment looking for the engine to rev. No such luck. I have put fuel cleaner in the car thinking it was fuel, but that didn't help. Also, I go the gas station of convenience. Not always the same place. I exhausted all of my limit knowledge, so I broke down and took it to a shop for diagnosis. They told me that they installed a vacuum tester and it revealed no leaks. They tested the Throttle Position Sensor and it was reading correct. They then tested the electronic Throttle Body, and it appeared to be the culprit. They changed it out this morning, and reset the idle. No Joy! This did not solve the problem. They told me that there were NO posted codes to work from. They were kind enough to not charge me for the part and labor since it did not fix the problem.

Now What??? They are out of ideas and told me to take it to the GM dealer for further testing. I am concerned that if the GM dealer cannot solve the issue, they will not be as nice and I will pay $$$'s for no answers.

I would severely appreciate any further advice anyone can give. Thanks.

P.S., I took video of it happening. As soon as I can figure out how to make it a smaller file size I will upload it.

[johnoski]

Uploading video to Youtube: Aveo 5 RPM Loss and Revs - YouTube



When watching the video, please watch the RPMs. Disregard the Tire Pressure Light. Soon after getting the sensors fixed, I picked up a nail. The tire has been fixed since then and problem remains. It is important to note that my foot stays steady on the gas pedal the entire time. When the RPMs go down, the car loses all engine acceleration, and MPH starts to decline. After a few seconds, it kicks back in and RPMs rev up for a second or two, then they fall again. I have watched the spot where they kick in and it varies. Never the same place, but usually between 1-2.5K.

[metroII]

Could it be the gasoline that your using? I mean, down here in PR i tried using this stupid gasoline called PUMA, but it was causing problems just like that. I put some fuel injector cleaner, changed the gasoline and filter, and it was gone. Usually i lost the RPM when i was slowing down then tried to accelerate again, the car would drop to 500rpms and then go like no problem

[johnoski]

Thanks for your comments metroII. I am in a small town, so my choice of gas come from about 4-6 main places. One of my initial thoughts was of a clogged fuel filter, but as far as I have come to find, the only filter is in the pump (which is in the tank). I have tried the cleaners and all of the different stations, to see if one place had bad fuel. I have put in cleaners, but no real change. Do you know if a clogged fuel filter or a faulty pump would post a code?

[petrified.rabbit]

is that a manual or an automatic? its hard to tell I think auto because of how is shifts, but it does shift which makes just watching the RPMs hard as its a shift drop.


imho I would replace the spark plugs. I only use NGK coppers in my car, replaced every 15-20k. I had our garage put in a set of autolite platinums, (recommended replacement based on the recall?) I couldn't make it home. I have not had the recall done yet though. Also my car feels considerably weaker when it is in need of an oil change as well as the quality of oil I use.

[johnoski]

Thanks petrified.rabbit. It is an automatic. The oil was changed about 1.5K ago, and I just put in the platinum's. I will look to replace those with the NGK this weekend when I have the car again. I went to the NGK website and they only list Nickel, platinum, and iridium. They all say they are copper core. Is there a specific one I should use?

[gothstone]

The NGK V power are nickel/copper and work the best. But on platinum plugs that car would run consistently poorly, the reving is a separate issue. Did they replace the actual throttle body, or the drive by wire sensor? Really sounds like the DBW has gone nuts. Other possibilities are the MAP sensor and IAC. Has the rubber tube air intake tube from the air filter to the throttle body rotted apart yet? If so replace it. If not, pull it off and clean the MAP sensor with electronics/contact cleaner.

[avguy]

I'm not seeing anything in your problem description which proves this is engine-related. You didn't mention any CEL/codes coming from this. If the engine were dropping out this much, one would expect that to be enough to trip the misfire counter.
Has anyone looking at your problem given any consideration to a transmission issue? There have been a number of transmission problem postings recently for 2009. Some of these problems have been found to be caused by coolant and transmission fluid mixing inside of the radiator/trans cooler. Has anyone taken a close look at the transmission fluid in your Aveo? (and the coolant as well). I'm certainly not saying this is your problem, but when multiple instances of the same issue show up on relatively young vehicles of the same year, it tends to send up the red flag.

[johnoski]

gothstone - Yes they did replace the throttle body. They told me that they tested the sensor at the pedal and it was sending the correct signals up the computer and it was sending signals correctly to the Throttle Position Sensor which in turn was trying to adjust the throttle (or something like that). Either way they said they tested the signals from the pedal to the throttle and they thought replacing the throttle body would fix the problem. I will have to look up the DBW sensor. The shop did not mention the DBW. Again, I will have to look up what the IAC is. I will check the air intake tube you mentioned tomorrow.

[johnoski]

avguy - I asked the shop if there were not any codes being posted. I agree that something should be posted. I hope it is not a transmission issue. That was the first thing my wife asked :/ My first thought was that if it was a transmission issue the RPMs would rev up, and not down then up to catch up. But again, I have a limited knowledge here. I am learning new things everyday. I will look up the transmission problem postings and see if the symptoms match up. Thanks for a new line of investigation.