My neighbour is a tech for GM and he said he saw this problem before... he says that the cause is in the intake manifold.

It has to do with our PCV valve that gets stuck.

This is why 2008 & up 2.4's have a different intake mani (but they flow less than 06-07 2.4's).


He might have a solution to our problem. He'll look into his things at work and let me know.

 

Mine is an 08

So the 08 intake flows less but it still makes more power? Guess the vvt is worth something then

Sure hope he comes up with something, mine has been pretty good for a few weeks, now this morning it is back to the same ****

 

bump!

for any kind of solution...

 

my auto 07 g5 gt is doing this. i was stopped and the rpm's just spiked and i about went out into traffic.

 

seems to me that this problem isnt just specific to chevy either, i had a nissan 300zx that did this, it pisses you off. and you know why the dealer doesnt know what the problem is? he's told to play dumb and sell you a new pcv valve. bullshit. nissan service man said, "you need a new pcv valve." i replied, yeah right crook, all i need is 10 minutes, an air compressor with a blower tip, and voilaa, brand new pcv. problem solved, cost nothing. i tell the stupid money hungry dealers **** off by rebuilding their electronic parts instead of buying one at their bloated prices. its easy and everyone on cobaltss.net could do it.

 

seems to me that this problem isnt just specific to chevy either, i had a nissan 300zx that did this, it pisses you off. and you know why the dealer doesnt know what the problem is? he's told to play dumb and sell you a new pcv valve. bullshit. nissan service man said, "you need a new pcv valve." i replied, yeah right crook, all i need is 10 minutes, an air compressor with a blower tip, and voilaa, brand new pcv. problem solved, cost nothing. i tell the stupid money hungry dealers **** off by rebuilding their electronic parts instead of buying one at their bloated prices. its easy and everyone on cobaltss.net could do it.

 

did it work on your 300zx?

 

Well my car does this every single time I drive it now

Here's what I noticed:

It starts happening only once the car has warmed up.
It NEVER (not so far for me at least) happens during the first three minutes or so of driving.


* My RPM stays at 1,500 RPM with the clutch in
* It revs up to 2,000 RPM when I decelerate
* It revs up on its own if I move up by a couple meters in traffic (to about 2,000 RPM)

* When I installed my LSJ throttle body, it amplified the problem by a lot and was pretty much impossible to live with

I HAVE GREY INJECTORS btw (2.4's have blue or grey injectors, for those that didn't know this...)

 

do you have your air conditioning on? if you do that is the answer.

 

no..
you barely see a difference with the AC on with our cars

AC does not make a car rev up to 2,000 RPM

 

is someone solve it with trifecta

 

....tuned area scalar?

 

Dealer was a blockade. They played dumb, of course. I let them clean the throttle body, as they had been begging to every time. No effect. Of course, it doesn't do it right away, so it is hard to catch with them in the car. Now they claim I need an intake manifold cleaning as part of regular maintenance. Bullshit. I've had over 100 cars, and the intake manifolds stay in-place, unless something breaks.
I'll try the PCV valve, although I would actually think it is the EGR valve that would be hanging. Either way, those are easy fixes.

Clean the intake manifold....

 

At -30*.....nope, pretty sure that's not the problem. Modern fuel injected car you will see little if any difference in the rpm when the ac compressor cycles.

Pretty much exactly what mine does, at least when it is doing it.
That has been the biggest problem, getting the problem to occur when the dealer has it in the shop. Not setting any codes, no other indication of any problems, performs very well....just this intermittent high idle bs.......

That, and the tires are almost gone in 30000km's.....but that's another story....

 

keep us posted, I am pretty sure that the proplem is linked to one of those things

BTW, we don't have a PCV valve...


Cleaning the intake manifold would make a lot of sense though.
I know there's a hole in the intake and our crankcase is connected to the intake manifold and sends dirty oil in there.
I've read of a Cavalier Z24 that had a **** load of oil in his intake mani and that caused it to idle high.

Anyway, try one of your fixes and let us know what works

 

are you sure that drive-by-wire is controlled by the BCM??
Can you back this up with something? The ECM would make more sense to me



my problem is getting worst and worst...... can't stand it anymore

 

Yep, talking out my ass. This info I got from a post on SSr programming on the programming forum. I just checked Alldata and both the Cobalt and SSr use the PCM and a dedicated module for the Throttle control (TCM).

 

Hey everyone, noob here!

I had this same problem on my standard 07 G5. What it ended up being was the clutch position sensor, I know wtf? Get the dealer to check it out, it might have popped off. But without it the computer will not know that the clutch is depressed and will hold, even advance RPM's, also it can cause codes if it tracks multiple successive shifts without using the clutch. It's an easy fix, and should not be costly, unless the sensor is garbage!!!

 

hey do have more details about this?

I want to try fixing it myself

Where exactly is this sensor located?

 

Yup! if you follow the clutch pedal up under your dash you should be able to see it. When you depress the clutch pedal it hits up against the sensor to register as clutch being depressed. If you press too hard on the clutch it can get pressed in and make it hard for the sensor to register each depression of the clutch, it's plastic, the threads are plastic so it's easy to knock out of alignment.

 

Well, there is no longer a valve in it, as the valve part of the PCV system was to keep the backfires from pressurizing the engine and blowing out gaskets. They replaced it with an orifice that meters the flow and cannot propagate the backfire pressure fast enough to matter.


The primary control is through the positive crankcase ventilation (PCV) orifice which meters the flow at a rate depending on inlet vacuum. The PCV orifice is an integral part of the camshaft cover. If abnormal operating conditions occur, the system is designed to allow excessive amounts of blow by gases to back flow through the crankcase vent into the intake system to be consumed by normal combustion.

This orifice sounds suspiciously small and sounds vulnerable to plugging. I'm taking my intake off tonight, so I'll update you on what I find. I'll be looking for this little hole.

BTW:
A leaking orifice may cause the following conditions:

* Rough idle
* Stalling
* High idle speed

 

So how did the pcv orifice look like?
Any news?

 

Well, the valve cover has a large hose connecting the valve cover to the intake track. This hose has a large opening, not some "precision orifice". I was expecting something inserted in the hose or air cleaner outlet duct (the large plastic box after the MAF). Nope, nothing looks precise there. I cleaned the entire intake manifold, and there is no chance in hell that there is any relation to the intake being dirty and the rough idle. The throttle body had been cleaned by the dealer and they did a crappy job. I cleaned it further and then cleaned the injectors and the intake area of the head. Also, I did find something interesting. There is a small metal insert in between the head and intake manifold. There is a precise orifice in this metal piece and it has a gasket of its own. The head has a hole there. It was somewhat restricted with carbon. I cleaned it and it is like new now. This looks like an EGR path. I see no other EGR route on this intake. So, the intake is only really getting dirty from the PCV blow-by. The head looked really quite clean, and there was no sign of carbon build-up, like we are used to seeing from high-EGR engine designs. Anyway, I won't know if this fixed anything for a few days, as this problem is intermittent.

I highly recommend you do this job by yourself and never pay for it. I was meticulous, and it took about an hour. You need a large and small regular screwdriver, a 10mm deep well socket, pliers, and carb cleaner (some rags too). Also, you will need two small flatblade screwdrivers if you want to take the seals out of the intake before cleaning it. I did, but then I cleaned the seals with the carb cleaner, as they are made to handle the stuff. You will want to remove the metal orifice and clean it, so you will need them for that job. The throttle body and intake manifold seals are all made to be reused many times. I have 50K miles on this and they look brand new.

I'll report back later this week.

Ok, DUH, I can't read my own posts. So next weekend I'll be taking off the VALVE COVER instead of the intake manifold (that is where the orifice is). I guess this will eliminate the Intake manifold and throttle body if this does not work.

I guess I was in denial about having to take the damn valve cover off...

Man, I'm getting old.

 

I have a 2008 Chevy Cobalt Sport, and it too does idle high when im comming to a stop, and then back to normal when im fully stopped. I have a CAI and an Apexi N1 Exhaust, and my check engine light was on before the mods. WTF???

 

reving at 1,500 RPM in traffic sounds extremely stupid guys...........

bump for a solution

I can't stand this problem anymore