Rough Idle at first start

[smcdmc]

I have a 2013 Genesis, 3.8. 81,000 ish miles (I work from home so I don't drive much, hence the low miles). I've noticed over the past 6 months that when I first start the car, the tach shoots up high and the engine seems to run very rough, almost like it is mis-firing. But then after about a minute, the tach drops and the engine runs smooth. It has never done the rough run before. I've cleaned the throttle body but no real difference. I've also noticed, and maybe I am being way over sensitive, but when driving and sitting at a stop light, I feel a little vibration in the steering wheel (I don't recall feeling this before but like I said, maybe I am being over sensitive). I'm going to clean the MAF sensor, going to do a valve clean with Gumout and do a engine coolant flush (never been flushed). Any thoughts on what might be going on?

 

[mikec]

Some emissions devices are triggered by engine coolant temperature or by signals from the Powertrain Control Module, either trips a small "vacuum switch valve" to connect one port to another or to switch one port to either of two possible other ports. It is possible a leaking vacuum hose is causing issues until a switching unit de-selects that hose and picks a different one. The 3.8 has quite a few vacuum hose connections if I remember correctly. Pop the cover off the engine and give the hoses a good looking over, flexing them and seeing if any are cracked/split especially near the ends. Often the ends plugged into the hot engine ports dry up first. A check I do to find leaking hoses is to use the spray carburetor cleaner (NOT BRAKE CLEANER) available at auto parts stores. Just make sure it says it is safe for oxygen sensors... that was an issue a few decades ago but, now that all cars sold since the mid 1990s have oxygen sensors pretty much all carb cleaner formulations have been re-done to be sensor safe. Anyway, right after the engine has been cold-started, spray the vacuum hoses, the gizmos they plug into, etc. and listen for any change in the sound of the engine - carb cleaner will make the engine stumble a bit. Any spot that affects the engine is likely a vacuum leak. Sometimes the leaks are loud enough to be heard!

If you do find any hoses that need to be replaced, don't just pull on them to remove them! Often the vacuum switching valves are plastic and the ports can be brittle on older engines. Use a knife to split the hose so you can peel it off the valve like a banana peel. You may find the leak is right at the end of the hose... banana peeling it and cutting off half an inch or so is enough to cure the leak assuming the remainder of the hose is long enough to reach. This is somewhat of a short-term solution though as the hose will still be old. It will get you back on the road for a while until you can buy fresh hose from the auto parts stores. It comes in a few internal diameters so you have to find the right size.

mike c.

 

[jep604]

Too echo, mikec, check everything overlooking for possible varmint damage. My 2014 3.8 V6 has very hard driven almost 245K miles and I haven't experienced this. She is garage kept and only stays outside at the hangar for longe periods of time when I travel. Drive the car like you stole it, it will thank you. Add Techron fuel additive at the next fill-up, makes a world of difference. Mileage and performance came back to the same when it has had 100K miles.