Will New Spark Plugs fix this?
 

I have a 2004 RX8 with 94,000 miles. I had the motor replaced at 71,000 miles along with new plugs and wires.

Recently my radiator went out so i had the mechanic install the new radiator. When i got the car back, it started doing a couple of weird things. First, when starting the car after being cold, it would behave like a lawn mower in that it would sputter to a start and idle very low. After a minute or so it would start to idle correctly and drive just fine.

Then after the car is warmed up, any time i would come to a stop light and put my car in neutral the rpm's drop to 0 and car turns off. Turns back on pretty easily but same thing will happen at the next stop light.

The mechanic did a compression test and said the car is at 105 pounds so it looks fine from that perspective but he could only find that the spark plugs were pretty dark especially on the cylinder that is throwing a misfire code.

My question is, do you think new spark plugs and wires will cure this? He wants to charge 210 for this and i want to make sure this will fix the problem.

Most people replace spark plugs about every 20k miles, so you are a bit overdue. The spark plugs cost $80 + tax at the store. They are very easy to replace if you would want to do them yourself.

When was the last time you had your ignition coils replaced? You didn't mention replacing them with the new engine and most people replace those every ~30k miles just as preventative maintenance.