RPM's really worrying me!

I have a 2005 Chevy Aveo LS Hatchback and it has a manual transmission.

I know this will be a lot to read but please try and help if you can. I would greatly appreciate it if i could figure out why my car keeps doing this!

Lately when i drive my car will get into this habit at any random time. I will be slowing down from any speed, from 10-55 mph, to a stop sign and take my foot off the gas and i depress the clutch to put the car into neutral and press on the brake to stop. Well, when i press in the clutch or even just pop the car into neutral without the clutch, my RPM's jump up to 3000 RPM's. Sometimes it will jump anywhere from 2000-3500 but every time i stop it jumps to the same RPM's as before. So it is consistent on how many RPM's it is jumping up to. When i say this i mean it will jump to a certain RPM every time i stop while the car is running on a certain trip to the store or even to another city. I could be driving for 10 miles in a stop and go situation and it never do any RPM jumping but sometimes it will just randomly start to jump RPM's in the middle of my trip and keep doing it until i get to where I'm going or it might stop after a couple miles.

This is greatly impacting my gas mileage and i really need to know what is wrong!

Thank you so much for reading and i hope to hear any ideas of what it could be no matter what they are!

Last night on my way home from work I was going about 55 mph and i pressed in the clutch and put it into neutral to slow down and my RPM's jumped from 2500 to 3100 RPM's. After being at 3100 RPM's for about two seconds it would drop straight down to 2000 RPM's, then after being there for about two seconds, it would jump back up to 3100 RPM's and start all over again.

One possibility might be the throttle position sensor. Have you ever cleaned the throttle body? The TB will collect a pile of gunk over time, and the TPS can get trashed out along with it. The TPS on the 2005 can be removed and cleaned without removing the TB.

I have cleaned the throttle body with throttle body cleaner and just replaced the TPS tonight but the problem is still present. When i am wanting to coast in neutral to come to a stop, i put it in neutral and i apply the brake, and the RPM's stay at the place it was before i put it into neutral. Sometimes it will jump up and stay at 3000 or 2500 RPM's but when it doesn't jump it just doesn't drop the RPM's until i come to a complete stop. Could it be a leak in voltage to something or a vacuum leak?..

Checking vacuum would definitely be a good next step. Some of the parts shops will loan or rent the testing equipment, and it's not too difficult to run the basic testing to check vacuum. But finding the actual leak can be a PITA, and may require a smoke test to locate it.

Okay, thank you! I will post any results if i find them!

I belive that the 05 has an all manual throttle body aka cable from the go pedal to the throttle body, I wonder if it's as simple as something along the cable routing has come loose and under the right conditions when you press in the clutch it catches the cable and actuate the throttle body causing the jump in rpm.

I can see your point but it happens continuously and consistently while in a single trip. Sometimes if i turn off the car for a minute and start it back up then it runs normally...

Do you have cruise control?

No, i wish i did though lol The car is a manual transmission and doesn't come with cruise control, the only way to get cruise control is by getting a cruise control actuator kit for it and running all the wires and cables and hooking it all up to the throttle cable and so on

One thing I can recommend is getting an ultraGuage, best $100 code reader you will buy, and it is a data streamer as well, and you can read what your tps sensor is seeing at that exact time, I have one and I love it. Buy one, hook it up and keep an eye on your tps that way and see if it's acting up next time the rpms jump on you.

And it may be a long shot, but try this:
The throttle body assembly is replaced
The throttle body is cleaned
The engine control module (ECM) is replaced
The idle air control valve (IAC) is replaced
Power disconnection (battery cable, ECM fuse, etc.) (Delphi ECM only)
Turn the ignition ON.
Turn the ignition OFF for 15 seconds.
Turn the ignition ON for 5 seconds.
Turn the ignition OFF for 15 seconds.
Start the engine in park/neutral.
Allow the engine to run until the engine coolant temperature is greater than 85°C (185°F).
Turn the A/C ON for 10 seconds, if equipped.
If the vehicle is equipped with an automatic transaxle, apply the parking brake. While pressing the brake pedal, place the transaxle in drive (D) for 10 seconds.
Turn the A/C OFF for 10 seconds, if equipped.
If the vehicle is equipped with an automatic transaxle, while pressing the brake pedal, place the transaxle in park/neutral.
Turn the ignition OFF. The idle learn procedure is complete.

Resurrecting this thread to see if a solution was found. I'm having the same problem. When I depress the clutch, the RPMs will jump up. Today I was in stop and go traffic, and it would consistently go to ~2000 RPMs when I would depress the clutch, or if I had the car out of gear with the clutch out. Putting the car in gear will drop the RPMs immediately, and from there they will stay in the normal range for the gear/speed.
I have an '04 manual.

That's a perfect case of a bad or very dirty Idle Air Control Motor. They're cheep and that's exactly what they do when they go bad. Vacuum Leaks also could be it, but those are usually a consistent higher than normal idle until it's fixed. The IAC is a Butterfly valve bypass port flow controller...... So when the Butterfly Valve shuts. It's a tiny valve that throttles open~shut fine tuning the tiny amount of air flow it needs to idle. If you get lucky you can take it out, clean it, it's shaft and the IAC port in the throttle Body very well. Throttle Body Cleaner is good stuff. Get around the Butteryfly Valve very well also. That's a calibrated gap and if that gap is dirty that that's one more thing the IAC has to make up for.

If you pull the Vacuum line off the Brake Booster while it's running It'll idle very high and the IAC should close. Than unplug the IAC and it should stay closed.. than plug the Brake Booster line back in and and if it idles down to normal than the IAC is bad and doesn't operate like it should or the shaft is dirty and it's gummed up and stuck open. If it idles down below normal and almost dies than the IAC shut like it should. Plug it back in and it should come up to normal idle. That's just a quicky test. But it may have intermittent issues with engine temp, It's a dirty electric part. If it was my car I'd buy a new one, clean everything in there and not bother with that 2 minute test.

Oh yeah, very important. The Aveo's air Inlet Flex Hose cracks. They all do. If it is cracked, than it's sucking air after the Air Filter! Causing a dirty Throttle Body and dirty IAC motor and unfiltered air to the engine/crankcase through the PCV. Those hoses are stupid expensive and it'll crack again. I used Black Rubber Gasket Maker on mine and my friends Aveo. I put a nice looking bead in every flex ripple and it will now outlast the car and after a few months of dust you can't tell it's not original.

Thanks for the info. I'll take a look at the IAC valve (assuming THIS is what you're talking about. I replaced the intake hose last year when I replaced the head. I noticed it had a leak when I was putting everything back together. Not sure if I was running it cracked, or if it cracked when I flexed it during disassembly of the car.
One thing about the idle speed is that while the RPMs are consistent when it's revving high, it's not consistent as to when it happens. It seems to be independent of outside temp or even engine temp. Sometimes it might do it when I do a cold start, sometimes it might happen when I've been driving for an hour.
I tried the above idle learn procedure yesterday, and the car was behaving afterwards (It was running about 900 RPM on the way to work this morning), but I'm sure I might be up to 2000+ RPM on the way home today.

just one clarification on this does it do it all the time or only some of the time? as one possiblity is (kinda hard to explain where it is but will try my best) there is a little clip that olds the throtle cable in place just to the right of the throtle body on the front this may be sticking caused by perhaps a freaying cable inside it happened to my mothers lanos was a case of taking the throtle cable off the body pulling back the protective sheefing and checking for any damage.

Quote:

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Originally Posted by marmite369

just one clarification on this does it do it all the time or only some of the time?

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Only some of the time. Yesterday, for instance, when I left work it would idle at 2000 RPMs. I went to the store and when I started back up, it would idle at ~900 RPMs for the rest of the way home.

Since we're all guessing here, I'll take a swag. Intermittent MAP sensor glitch affecting ecm load calculation. Any codes stored or engine light?

HTHY-- the krusty mechanic.

And of course it could also be a vacuum leak like Lola and the others said, The IAC is really a controlled vacuum leak. I was trying to provide a fresh perspective.

Quote:

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Originally Posted by JusteR

Since we're all guessing here, I'll take a swag. Intermittent MAP sensor glitch affecting ecm load calculation. Any codes stored or engine light?

HTHY-- the krusty mechanic.

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No light. My scanner cord is MIA. Need to find it and hook it up to the PC.

Quote:

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Originally Posted by JusteR

And of course it could also be a vacuum leak like Lola and the others said, The IAC is really a controlled vacuum leak. I was trying to provide a fresh perspective.

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Yeah, gotta check for this, too. I didn't have time to look at the car over the weekend. I had to fix my wife's cruise control (Someone *cough*me*cough* accidentally left a sensor unplugged last time he was checking something under the hood).

Wanted to give an update (for this thread I hijacked). I pulled the throttle body off and cleaned up the IAC and the TB. I replaced the TB seal while I was at it. None of that changed anything with the high idle. It had been very consistently keeping the idle about 2000 rpm when at a stand-still, and not really dropping below that while driving, either. Occasionally, it would drop below that when I put the car in 1st and gave it just a little gas.
Anyhow, I did the suggestion from earlier in the thread where I unhooked the brake booster line from the intake manifold, unplugged the IAC, and then put the brake booster line back on. The RPMs didn't drop like they should have, indicating a bad IAC. What's weird, though, is that the past two days since doing that, I haven't had any issues. So....not really sure what the deal was/is. It's been working fine, idling at the correct speed, etc.
I've also tested for vacuum leaks, and can't find any.

I've got my fingers crossed, hoping that the issue won't rear its head again...but I'm sure it will.

Sounds like the IAC was carboned up? And cleaning it and running it open and closed helped... only time will tell. Hope I helped. I appreciate the follow-up.

Haha no worries about the hijacking! I have been busy and haven't been getting any notifications on this thread for some reason. I have tried checking for vacuum leaks by spraying brake cleaner on all of the vacuum hoses and also blowing cigar smoke all over the hoses and I found no leaks. I have checked and cleaned the butterfly valve in the throttle body and the IAC and also replaced the IAC and still having the same problems. It doesn't matter what temp the engine is at or the outside temp. I am planning on trying the break booster line disconnection sometime soon and I will report back on what happened.

SpiffWilkie Any update on how it has been acting since you did the break booster procedure?

Holy $hit - sounds like you're saying this high idling has been happening with your Aveo for almost a full year????

Idk how u can drive it that long with this dam problem. My automatic is having this issue and I cant stand it. Been going on for 3 weeks now. Have yet to find a solution for this issue.

Yeah it just goes off and on, but when it is on it seems to never go away until I am done driving it for a bit. It it is very irritating when every time I switch gears the engine revs up to like 3500 RPMs and then bogs back down when I put it in gear again. I'm afraid the clutch is going to got extremely torn up because of it. And yeah, I would love to get it fixed but I have had two different shops run diagnostics on it and they bot told me it could be the IAC but i already replaced the IAC and nothing changed. They don't have any Idea what it is and they said they have never seen this problem under these conditions. It is soooo irritating also when coasting up to a stop light next to someone and they think I am trying to race them by revving my engine when i'm not, or even coasting through the parking lot, people think I am revving my engine at them while they are walking and it is just annoying haha I get so pissed off and just beat the **** out of the steering wheel when it just continues and continues to do it cause I have no flippin clue as to how to fix it... haha I have even tried turning my car off while coasting and while stopped (once it revs down all the way) and restarting it but it just jumps back up to the same high ass RPM's lol

No one in two shops could figure out this problem? Another example of why many here try to DIY whenever possible.
Have you tried the brake booster test that was posted above? Based on what SpiffWilkie wrote, it seems definitely worth trying. Also, have you carefully examined the TPS and IAC wiring and connectors? There was a thread a while ago (that I can't find now), where someone posted that a dealer replaced one of those connectors. Fixed their problem, but I don't recall the exact details on that one. How about the old favorite test spraying a bit of carb cleaner around the TB, manifold, and hoses, to see if there's any change in idle speed?
There was also a post recently from someone who found that the rubber ends of the map sensor connector were cracked. That doesn't seem like a possible reason for your problem, but it might be worth a look anyway, especially since it will only take about 10 seconds.
RPITA you have there :angry7:

I tried the break booster test today and the car idled back to normal after I unplugged the IAC and reconnected the break booster hose so that tells me my IAC is broken or gummed up. I also found that there is a crack/tear in my intake flex hose so I took it out and removed the Intake Air Temp Sensor and I am soaking it in dawn and hot water to get it cleaned up. I am going to use some Flex Seal to hopefully seal up the intake hose once it is fully dried. The unfiltered air could have made the IAC gunk up but the rest of the throttle body is clean so i'm not sure. When I put my finger on the hole on the inside of the throttle body behind the butterfly valve where the IAC regulates the Idle air there was a brown/orangish colored oil or something that got on my finger. I don't know what that could be but I am going to take out the IAC and hopefully clean all of that up with some throttle body cleaner. I also ordered a new IAC and should be replacing that tonight to see if it is fixed. I should have it all fixed up by tomorrow around five. I will continue to update everyone on here when I find anything new.