Hi, what would be the next thing to replace after plugs. Car is still giving code po300. My assumption would be the coil packs. Before plugs code was for misfire in cylinder 6. Thankyou

 

What did coil tips and spark plug boots look like when coil packs were off? You really need scanner to check out, or play expensive game of guess. Taking to dealer/shop maybe your best option.

 

Hi; Is the car using more oil than normal? I had a 2000 STS V8 and had a miss problem when the car was started cold causing error code. Took to dealer and they replaced the plugs and wires/boots etc. Car was OK for a couple days and then started missing again, took it back to the dealer and they told me that I have a blown head gasket and water was getting in the cylinder causing the miss, however I never lost a ounce of water! That's why I asked about oil consumption, I believe oil not water was getting in the cylinder causing the miss, I was using 1 quart of oil every 1000 mi. After the car warmed up, burning off the oil, everything was fine.

 

if you look in our FAQ section, you will find a exhaust gas in coolant test, inexpensive.
if there was oil consumption, there may well be rings sticking.

there is a cleaner for that, as well as the great WOT .. look in our FAQ section

 

Thankyou for the advise. I will be doing the coolant test. The car does use a lot of oil, about 1 quart every 1000 just like pjbizjak but does not appear to loose coolant. I've started the WOT but no results yet and will be using a cleaner also....oh and the rubber boots and coil tips looked very nice and clean.

 

I have a 1996 cadillac STS with Northstar motor with 115k on it. Other than normal maintenance items, car ran fine a long time, wires replaced at 100k. Recently car started running extremely rough at 700 rpm idle, smell of gas, huge drop in gas mileage, 0300 misfire codes, check engine light, etc. I changed gas, no luck. I installed all new plugs (about $20) and cleaned up the ignition coils. One was pretty beat up so I wire brushed the corrosion off it. This took care of the problem temporarily but I was soon back to same old symptoms. Did some online research and shopping. Coils are EXPENSIVE. I found a seller on amazon and bought all 4 coil packs for about $60. Just got them today. Spent an hour and a half replacing all of them. Eureka!! Hooked up battery, test drove car about 6 miles. No rough idle at 700 rpm, can't even feel it running. Gas mileage (city) shot back up to 17mpg. Yes I realize it's a short test. Misfire codes cleared, no check engine light. Looks like problem solved. Today is a good day. Btw changing coil packs is a fairly easy job. 7/32 socket and extension and disconnect battery. Just make sure you don't reinstall your wires to the wrong coils.