[prlj91]

I've had my GT a little over a month, and I love the car. It performs well, and it's much more fun than my previous 3.9! I've got couple problems though, the main one being my bouncy idle.

The car, while in park, idles fine for the first 30 seconds or so, but after that, the RPMs bounce anywhere from about 200 to 700, then sometimes up to 1000, and the engine makes a surging sound. As soon as I come to a complete stop, it sits at a steady idle for a bit, then begins to surge a little. Also, pressing the brakes in even further when I'm stopped causes the idle to dip. It came with a K&N PFIK CAI on it, and I've never had a car with one before. To me, it sounds funny, but I'm not sure. It makes a sputtering sound occasionally, and I wonder if it's not installed correctly? Maybe there's and issue with it affecting the idle? I've already cleaned the MAF and IAC just to make sure those weren't malfunctioning, but it hasn't helped.

As a side note, the traction control acts funny. Basically, I accelerate at the on ramp, not hammering it, just normal acceleration, and then my TC kicks on and whines like crazy until I slow down. I literally cannot reach highway speeds unless I turn my TC off...which isn't a problem, but I'd like to know what's happening. My previous 3.9 '04 never did this no matter how hard I slammed on the accelerator.
It might be worth mentioning...Every time I start the car, I back out of my spot, then kick into drive. Right after I accelerate forward, I hear a little whine that sounds just like the TC, but only for half a second, and then it stops.

Thanks in advance for any suggestions!

 

[newponyboy04]

Bouncing idle could be a various of things. I would first check for any vacum leaks.

 

[prlj91]

I've checked but haven't found anything yet. I've been told that leaks you can't see with the naked eye can cause this problem though. Any idea why the idle dips when I press the brakes in after I stop?

 

[newponyboy04]

A vacum leak ints a fluid leak. Check your vacum lines with carb cleaner. Spray a bit in small area and if the idle surges then you got a leak

 

[JonR2006]

The reason why the engine RPM lowers when the brakes are pressed hard is because the brake booster uses hydraulic pressure from the power steering pump to provide assistance in braking (Hydraboost Brake System). When that assistance is needed it puts more pressure on the Power Steering Pump causing more parasitic drag on the engine, lowering RPM just a bit.

As far your idling problems, just because you cleaned the IAC doesn't mean its not at fault. Most of the time, if the IAC bad, cleaning it doesnt matter. It will need to be replaced.

If the idle is as bad as you say it is, then surely your CEL is on and is throwing the code telling you the problem. Report back with codes and we can help further.

 

[prlj91]

No, no code. If there was, I would have mentioned it. The idle isn't bad in the sense that it affects the car's performance, but it's obvious it shouldn't be doing it. The reason I mention the brake is because it dips very low when depressed. I could replace the IAC though and see if that solve the issue. I tried spraying brake cleaner around and on the vacuum hoses as suggested with no results.

 

[racin366]

Try removing and cleaning the IAC

 

[kiliona]

the EGR valve is also a very likely candidate for a bouncy idle. As someone else said, take a can of carb cleaner and spray it around anywhere there could be an intake leak. An intake leak is when the vacuum caused by your engine sucking in air pulls in air from somewhere that isn't your air filter (IE after the maf which is why it affects the idle, your maf doesnt register the unmetered air so it causes issues). Anywhere you have a vacuum line there could be a hole or a split, check them and spray carb cleaner on them. anywhere around your intake manifold gasket or the base of your throttle body could also leak, as could a number of other places.

The reason carb cleaner will help is if the carb cleaner gets sucked into the engine due to that vacuum leak/unmetered air thing i was talking about, It will dilute the air fuel mixture and cause the idle to drop (or raise if the cleaner contains ether which is essentially starting fluid).

I actually like using an unlit propane torch more