I have a 07 LS and an issue along with it (but who doesn't). Well, since I've had the car I've had not many problems with it, then I put on a CAI, then kaboom, CEL. Rich code, P0405? I think? Well unimportant. I took it to the dealershit and they said oh the reason you're getting a CEL is because there is an open campaign (code for recall) for an ECU reflash. I said ok super, they reprogrammed it, and instantly, CEL back on. So I took off the MAF cleaned it off, and it never came back on; go me right?

However this is where is gets fun. Ever since I got the car back, when I drive the car, get on it, only slightly, and let off the gas the RPM's are extremely slow coming back down, MAINLY only when the brakes are applied at the same time. At times the engine will keep at about 3k - 3.5k. I was thinking the IAC is sticking, possibly. But then as I look around the engine, everything looks just super, and I can't get the problem to reproduce in the garage, I'm thinking only under load.

Anywho, has anyone else encountered such an issue in 07's or otherwise? This one has me puzzled. I think I've ruled out a Vaccuum leak because of the intermittantcy. Would a crimped vacuum line for the brake booster cause such an issue?

Any info would be greatly appreciated. Thanks!

 

for one.. the MAF is SUPER SENSITIVE... a bump and its fucked...

take it for a ride with one of the garage guys, thats what i had to do for bad tires

 

I think it might be part of the reflash,mine holds a high idle (over 1000 rpm )until the wheels slow down to a certain speed and then the idle drops.This is with the clutch in and rolling slowly to a stop.
But in your case its pretty high,idle control valve maybe sticking ?
Just guessing though.

 

I too thought of the IAC as I posted, but looked for it to clean it all out and what not, but still no luck! I don't even think this car is equipped with such. This isn't your every day issue. Like I said, I'm puzzled.

 

TB could be sticking...

 

Sounds like a leak somewhere. Rich and lean trim codes are most commonly caused that I've seen from bad sensor calibration (probably not the case here) or from some type of air induction leak.

Also, there is no IAC. Since these are electronic throttles, the PCM simply commands the throttle body slightly open to maintain the desired idle. Basically, the PCM has direct control over RPM. If for some reason it would differ from what is commanded, it would immediatly throw you into limp home mode.

 

Ok, I'm glad I was right in the back of my mind. I didn't see anything at all that could resemble an IAC, so I figured there must be a leak.

However! The veh did do something very odd once, and once only. I got onto the road, it just rained and I had the CAI installed. I kinda got on it, big hesitation and studder, then it died out. Every time I would engage the clutch it would bog down and die out. But then without the engine under load, it would rev ok, but not smoothly by any means.

Ever see that happen? lol.

 

What exactly were the trouble codes that were pulled from the computer? P0172 would be the fuel trim out of whack. Anything else?

 

Actually, what you are describing sounds normal. (I know, you think I'm nuts)

Part of the engine program for these cars is a regulated decrease in RPM when suddenly letting off the accelerator. The drive by wire throttle keeps the throttle open and closes it slowly so as not to suddenly jerk the engine to idle. My car has done that since day one.

 

What junk. haha. I would say there must be a ratio of which it closes, either by only time allowances or throttle position per m/s or something. If this can get reprogrammed, I'd be happy. I never ever noticed this before the reprog, and that's what pisses me off the most, that they would reprog something as stupid as this. That's why I thought, no way, this has to be a fault in the system. Well I'll have to check the invoices and update yall. Thanks for the help thus far!

 

My car does this too.

If I shift close to redline and then get off the gas close to redline, clutch in, it'll rev real slow down.

If I put it in neutral, clutch out-clutch in, it'll go down regular.



I thought this had to do with the FI pushing so much fuel into the engine, then the driver cutting it off. Cutting it completely off when be harsh on the engine wouldn't?



5-speed right, not an automatic? Automatics do this too, you just don't notice it as you are not in control of the clutch.

 

So if this is true of the Cobalt, why all of a sudden? I've never noticed this before, and ever since I dicked around with the vacuum lines and found a crimped booster line and straightened that out, it dissappeared. Very odd.