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

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.

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

http://www.youtube.com/watch?v=X_BPgQZMcq8

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.

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

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?

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.

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?

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.

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.

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.

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.

So, I just checked the A/T fluid based on a transmission post I read about not enough fluid. Apparently mine is over-filled. Not sure who filled it (I did not), but the fluid covers the entire portion of the dip stick before the twist (well past all the holes). This was check cold (not run for over 24 hours). Also the fluid was not a clear pink color. It was more a dark brownish pink. It appears it needs to be changed, but can it being over filled cause these symptoms? Anyone know?

Quote:

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Originally Posted by johnoski

... Apparently mine is over-filled. Not sure who filled it (I did not) ... Also the fluid was not a clear pink color. It was more a dark brownish pink. ...

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Based on what you found, it seems there's a good possibility the tranny fluid has mixed with coolant. You could try calling your local Stealership, tell them you found coolant mixed in with the tranny fluid, and see what their reaction to that is. Based on a prior post from another member, I believe that Chevy is well aware of this fluid mixing problem in the 2009, and probably would like to keep it as quiet as possible. Perhaps they might be willing to repair or replace the tranny for zero or at least a reasonable price.
If they claim to be unaware of this problem, I would send the fluid to a lab for testing - I think Blackstone Labs does a basic test for $25, which includes checking for coolant. But do not change the fluid now, because you will then no longer have the evidence of this problem, should you decide to pursue it further with Mother Chevy.

***NEW INFO*** (12/26/13)

This car is no longer under warranty. Draining the Tranny fluid, changing the filter, and cleaning out the pan, did not help the issue at all.

While I was with extended family over the past couple weeks, an uncle of mine suggested that it could be the fuel pump starting to go bad. He noted from his experience, that when they start to go bad, they will work fine at first, then after a few minutes they get hot and start acting up and can lose pressure. So I did a little testing of the fuel pump. Here is what I did:

1. Pulled up the back seat and removed the cover exposing the pump connections. I connected leads to the Positive and Negative wires (Brown and Black), and drove the car while monitoring the voltages present. When the car is driving normal or accelerating, the voltage is at a steady 13.78 +/- 0.02 volts. When I am braking or at a stop light, the voltage drops a bit to 13.62 +/- 0.02 volts. This seems normal to me since the higher voltage is when the pump is under stress, and the lower is when the pump is not. If I am not correct in this logic... please correct me :) When it did act up the voltage was all over the place. Sometimes it dropped between 13.5-10.5 volts, and sometimes it only dropped about 0.0 to 0.3 volts.

2. Second, I did a voltage drop test on both the positive and negative sides of the fuel pump power circuit. On the positive side the voltage was 12.59 volts with the engine off, and 0.46 with the engine on. This was obtained by connecting the positive lead of my multi-meter to the positive terminal on the battery, and the negative lead to an extension connected to the positive wire on the pump (brown wire). On the negative side the voltage was 0.00 with the car off, and 0.40 with the engine on. The negative was obtained by connecting the negative lead to the negative terminal on the battery, and the positive lead to an extension connected to the negative wire on the pump (black wire). Again, I think this is normal, but correct me if I am wrong.

I am beginning to believe this is a fuel pump problem. Since the pump is like $350-$400, I would like some other opinions before I pay for a new one.

Also, the CEL finally came on. I never thought I would be happy to say that. The plan is go an have those checked tomorrow at a local shop.

Thanks!

I wouldn't go by voltage to determine a good pump, it will vary based on rpm in the aveo, just as the headlight dim and bright with rpm the signal power to the fuel pump will fluctuate. and based on your attempt to get the voltage as an issue, the fuel pump relay would crap out first.. most likely. I had to replace my fuel pump in my car, i think i had maybe 5000 miles at the time? it just quit all together.

you need to check the fuel pressure at the rail to determine if you have a power loss from the pump.

have you replaced the spark plugs yet? i skimmed back through the post and didnt see it. IF not that then you need to get rolling data of a scan tool to hone in on things like a dirty maf, or bad o2. (just not bad enough to cause a cel).

I did put the spark plugs in that you and gothstone recommended. No luck with that.

OK... Took it by the local garage to have the codes read. There were a lot of 02 Sensor Bank 1 codes. A single Map failure was found mixed in. I did not think to get the Pxxxx number until after I left. The tech cleared the failures and reset the CEL. Hopefully it will come back so I can get an actual code number. I just hate driving it. The car has gotten much worse over time.

It not loses the RPMs all the time. It is fine for the first 1-5 minutes, then it fails for the next 15-20, works again for about 5 then fails again for another 15-20. Thankfully, most of the times I need to drive it, it is only 15-20 minutes at a time.

With that type of code it does now seem like an engine-related issue and not the transmission. Depending on which code(s) are actually set, I'm wondering about the new cats that the dealer replaced (or at least said they did). Do you have the paperwork showing which cats they installed? I've read posts from others saying that an aftermarket cat didn't work properly, and eventually had to be replaced with the better one (i.e. more $$$). But perhaps it's just simply that one or both of the O2 sensors are bad.
It's unusual for a cat to go early like your's did, and whatever took them out might have done the same thing to those sensors. That would at least be a relatively inexpensive fix. Get all of the codes as quick as you can, or maybe just take a shot at replacing the O2 sensors, because you want to get that rough running fixed before it causes additional problems.

I read that the CAT or O2 sensors wont cause issues like this. Was that inaccurate info? Also, I read that a way to check the MAP sensor is to start the car and remove the power cable from the sensor. If it acts the same, then the sensor is bad. Also, when the car is on, but not running, it should read about 4.5 to 5.0 volts. When idling, it should read about 0.5 to 1.5 volts, and when under stress (higher RPMs), the voltage should rise with the RPMs. Is any of this accurate?

Being primary contributors in the closed loop, I would think that bad O2 sensors and/or cat could be the cause what you're seeing. But it could of course be other things as well, which is why it's important to get the exact codes in the order they're read, to help diagnose the problem.

the first O2 could cause crappy driving conditions. As learned by experience the O2 sensors should be pulled when welding the exhaust cus the excessive heat could kill the sensor.

FINALLY... Problem solved! :D For those who said it was the O2 Sensor... You called it RIGHT. I tested the O2 sensor on the manifold and believed it to be bad. I went ahead a replaced it with an OEM part and problem is gone! I can finally drive it safely again.

Thanks to all for your assistance and recommendations.

Hey bro. Do you replaced downstream or upstream sensor?

Quote:

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Originally Posted by mr.nestorramirez

Hey bro. Do you replaced downstream or upstream sensor?

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This thread is almost 9 years old and person you are asking hasn't been around in 8 years. Suggest you start a new thread describing your issues and what you've tried

The O2 sensor on the manifold would be upstream, I have the same issue, I cleaned my O2 sensor and it ran better but still having same issues only less, I think I'll buy a new one.