Ok I used Seafoam today. I put a whole can in the gas tank and 1/2 thru Brake Booster line and other 1/2 in crankcase. Now it very rough idle and then when it's about to stall it kind of "surges" and returns to normal. There is an engine light on for voltage problems to the O2 sensors? Also the thing that scares me the most is that when accelerate lightly from a low speed it won't accelerate and kind of big down and then I hear a loud knock coming from the engine and it will accelerate again and no knock. I drove it a total of maybe 50miles with the seafoam in it then changed the oil with Mobil 1 filter and Mobil Super High Milage. Please I'm scared I broke something and don't have the $$$ to fix it. I just spent 2K on the truck for various parts. It's a 5.9 with 200K miles if that helps...

 

What exact codes are you getting?

 

P0132 and P0138 code.

 

pull the spark plugs, seafoam can gunk them up, and if they arent firing right they can throw codes (i believe those are O2 sensor codes you referenced).

start with that, if thats not it you may need to replace the O2 sensors.

 

Would fouled plugs/ 02 sensors cause the rough idle and knocking? The knocking is my main concern....

 

rough idle for sure, if the fuel isnt being ignited by the spark i could see it causing knocking


short answer, yes assuming they are bad enough it is possible.

 

So you don't think its something major like a broken rod? If I drive it with the knock will I damage it further or do I wait for it to go away. Its only occasional.

 

seafoam is not going to cause a broken rod i promise

an occasional knock is not good, but will not (in most cases) cause any immediate damage, however it does mean you should be looking to fix it immediately, and not be driving around in it more than you absolutely MUST.

 

Ok, what you just said has relieved me greatly! I just let out a huge sigh of relief. I trust your opinions as I can see your a highly respected and knowledgeable source. But now...How will I go about fixing it. I dont have to worry about driving it but How do I go about fixing this knocking? If I change the plugs and/or the O2 sensors will the knocking GO AWAY? Thanks again Shrp for your helpful answers. I'd still be freaking out if not for you...

 

Probably too much seafoam in the gas. That would cause a knock, try some higher octane gas.