gocchin

So I was at a garage that specializes in Evo's in Yokohama just under 2 weeks ago where I had a full checkup of my car's condition and a baseline power run on the dynopack.

Tuner suggested it was time to change the plugs so he went ahead and put in HKS Super Fire plugs 1 range colder (8) than the stock ones that were in there.

After leaving the garage the car shuddered a few times at stop lights and it seemed to misfire during WOT on the freeway and when boost came on it felt like the car had no power.

I thought perhaps I need to reset the ECU so when I got hope I did that and the next day I let it relearn idle.

In the following days, the car continued to idle between 1400 and 2000rpm on cold starts and would do this for at least the first 10-15 minutes of driving after which idle would go back to just under 1000rpm.

The misfires and inconsistent power were still present. I was almost afraid to go into boost as I would hear the turbo spool up and hit 1.5 bar but sometimes I felt as if I was going nowhere.

After about 180 miles I pulled the plug to go back to the stock NGK's. Idle back to normal, car still feels smoother but got a few misfires today (came from the engine bay).

I have pretty basic bolt ons, cat back HKS exhaust, HKS Intake, HKS Intercooler Piping, HKS EVC-S EBC (which I turned off since I left the garage for fear of overboosting).

Here are the HKS plugs after only 180 miles. It appears to be carbon fouling? Am I running lean? Something else I should look for?

Thanks in advance for any help you can provide.

HKS M40il (#8) plugs after 180 miles:

i8acobra

Carbon = rich. This can be cause by plugs that are too cold. "Cold" plugs have an electrode that doesn't extend into the combustion chamber as far as a hotter plug, leading to incomplete burn if the car is not properly set up for the colder plugs. If you went back to the "9" plugs, it should clear up soon.

gocchin

I do think the HKS were too cold. Took forever with them for the car to warm up and get normal idle then ran like crap at WOT.

Gone back to stock plugs and as I said misfired a couple of times but it could be just settling in.... I hope.