I’m troubleshooting a misfire issue in my Veloster Turbo that occurs only on cold starts. It misfires on cylinders 1 and 2, and I get rough idling only in the morning upon the first start. Once it warms up, the engine smooths out and runs fine.
Symptoms:
Cold Start Rough Idle – Runs rough only during the first startup of the day.
Cylinder 1 & 2 Misfire Codes – Initially, only cylinder 2 had a misfire, but now cylinder 1 does as well.
Jittering When Creeping Forward – In the morning, when I release the brake without pressing the gas (such as backing out of a driveway or rolling forward), the car jerks badly.
Intermittent Jittering at Low Speed – Occasionally, when slowly rolling forward (like in a drive-thru), I get similar jittering.
Repairs Done So Far:
New Spark Plugs – Replaced all plugs.
New Coil Pack for Cylinder 2 – Misfire persisted, and now cylinder 1 is also affected.
I put Techron Fuel cleaner hoping maybe an injector could be clogged from carbon? Its got 122,000k.
But whats weird is after the morning roughness idle the car shifts fine. Not stuttering no fluctuations in rpms. The engine idles very smoothly. And gets up and goes pretty well.
I’d have the intake system inspected for carbon buildup, a common problem on these GDI engines. If it’s the problem Techron won’t help, may not have helped prevent it, either. Only a thorough cleanout will work.
How many fuel injection/intake services has the car had in 122,000 miles? If it were mine it would have had the intake and injection service done 4 times by now.
How does the engine run under load, as in merging on to the freeway with the pedal to the floor?
Okay. Maybe have it walnut blasted? Is it possible i could have a leaking injector where it sets over night? I thought about the valves but wouldnt i be seeing that roighbidle no go away? But only upon startup? I wanted to ask is it possible an injector could be leaking over night after it sits to much fuel is on the cylinder head? Then when i start it up its got to burn that fuel off?
No its response to throttle is great. It runs and idles fine has no problem. Its just only in the morning with that first quirk. I can reset the code it will go away and stay off. But will return after that next morning start up. The valves have not be done yet. I run techron in the fuel every 3,000 miles.
You engine is direct injection so the Techron might keep your injectors clean but it does nothing for carbon buildup on the backsides of the intake valves. Direct injection fuel injectors spray fuel directly into the combustion chamber… it never sprays on the backsides of the valves to keep them clean.
There are chemical treatments that are introduced into the intake manifold that help keep the valves clean. Buildup can cause problems like you are having. A boroscope into the intake manifold can show you if the valves need physical mechanical cleaning… solvent and scrape or walnut blasting. I’d try a chemical cleaner first… something like this;
I bought some GDI cleaner removed the throttle body and had my friend rev it while i sprayed it in. It seemed to have helped my turbo a bit. But the codes never retreated nor the rough idle in the morning. This light is driving me nuts..and the bad jittering because its running fine after that. I can set a drink on the engine and it barely vibrates. I was trying to edit my post i accidentally deleted. But is it possible an Injector could be leaking over night? And then to much fuel is on the cylinder head and its causing that morning craziness. Although i need to get the valves done, wouldnt i be seeing that rough idle through out the day? If a valve wasnt able to open up fully like its supposed too?
That would give you a long crank time in the morning at first start.
No, too little fuel but only initially.. seconds.
Not necessarily… Cold start is a different condition than a warm idle.
That isn’t what happens. The valve opens fully because the cam opens it. The issue is obstructed airflow past the valves. You need to have a look inside. Either scope it or remove the intake manifold and look.
Yes Only those 2 codes. P0300. “Multiple misfire within a time period” can you guys tell me what the average price of having a walnut blasting would be? Also thank you guys for being so quick to help!
So i called around and only found 1 shop in North Carolina that can do it. They wanna scope it first to make sure thats what it is. He said it is pricey. They haven’t done it alot. But they have done it before…i also called another shop and the guy said it sounds like water is getting into the cylinder? Is this possible?..
Yes. I have replaced a few high-pressure fuel injectors because of leaking after shut-down. Inspect the spark plugs, the cylinder with the leaking injector will usually be black with carbon deposits on the center electrode insulator.
You can inspect the cylinders while warm with a borescope for the presence of fuel or coolant.
