Rough idle 2002 dx

[t5contradiction]

Hey guys,
Just recently picked up a 2002 dx with 150k. The car runs and drives fine but idles rough. I get a CEL for random misfire p0300. I replaced the plugs, wires and coils, no dice. Cleaned the throttle body and the maf, still nothing. Replaced the egr valve, iac, tps sensor and still nothing. The only difference is that now the car will idle good until it warms up, once hot its back to misfiring. THe timing belt is brand new and I checked. One thing I did notice when double checking on the spark gap is one of the plugs is darker then the rest. Any ideas? I cant get the car through the smog test with the check engine light on.

 

[lolwut]

Is it automatic or manual? Can you post a picture of the plugs?

 

[t5contradiction]

Is it automatic or manual? Can you post a picture of the plugs?

its manual. Plugs are back in the car. All new, 3 of them are tan-ish color (normal) but the other one is black but not fouled. Excessive fuel? No oil in the spark well. I also replaced a coolant temp sensor today with no improvement. Again it will idle just fine until it warms up and then sounds like its misfiring with the damn p0300. Dmv wont give me the tags/registration until I run it through emission.

My other thoughts are crank/cam sensor before moving on to the fuel.

 

[lolwut]

From experience having a cam sensor go bad, I dont think its that. My car would barely start and I wouldnt be able to drive it more than 20 yards without stalling out. I would lean more towards that cylinder with the blackened spark plug. If it had excess fuel (running rich) you would be able to see it in the exhaust most times. Give it a fuel treatment and see if it helps. Also check for vacuum leaks if you havent already.

 

[t5contradiction]

Checked vacuum lines, all is good. I put seafoam in the gas tank yesterday. About half way through with it. Should I move on to sourcing out a fuel problem?

 

[lolwut]

The duct work for the intake is crack free as well? Did you put any Seafoam through the brake booster vacuum line?

 

[t5contradiction]

intake boot is fine. seafoam in the gas tank only.

 

[lolwut]

Id advise putting it through the brake booster vac line and in the crank case as well. 1/3 of a can in each in accordance with the directions on the can. Let it idle for a few minutes, then take it for a drive. Dont be scared to get down on the throttle and clear all that s*** out. Just be sure to change the oil afterwards as seafoam breaks down components in it. Anything helps at this point

 

[t5contradiction]

So I put half a can of seafoam into the crank and it got worse and then slightly better....still misfires. This time I got the code p0300 and p0303 so I know its an issue with cylinder 3. I did notice something today. One of the coils had a number 02461 stamped on top but the other had 02241. They are both bwd from advance auto. Shouldnt they both be the same?

 

[t5contradiction]

Also, now I can feel the car misfire sometimes under "hard" acceleration

 

[lolwut]

Half a can sounds like a bit much, but as long as you changed the oil afterwards it doesnt matter (I cant stress that enough). Im not sure about the numbers stamped on them, call the store and ask or research the part numbers online. And at least you know which cylinder is giving you s***. By chance, was that the one with the iffy spark plug? Aside from valve s***, it could be a bad fuel injector, loss of compression, etc. If you have the means to do a leak down test yourself, do it. If not, you might have to cave in and take it to a shop.

 

[xtreme velocity]

My car is doing the same thing yours is pretty much but without a check engine light. I done some work to a car today at a shop with some extensive research. I found problem for this car was the cam sensor. Problem fixed. No more cel or rough running. From research cam sensor can cause rough running or no start. But in a sense that may not be your problem since you are only having trouble with cyl 3. Might try clearing codes and switching injectors and seeing if the misfire changes. That will at least rule out the injector issue instead of buying new ones. If not check for faulty plug by switching plugs around. It's extremely rare, but can happen. I hope this helps! Still trying to narrow mine down. Lol but I don't have a cel on so I don't have any direction to go. Lol

 

[talltim]

Bad plug wire?

 

[xtreme velocity]

If inside the rubber part if plug is not making good connection it can defiantly cause misfire.

 

[talltim]

I have had to troubleshoot this issue many times with my cars and it can be one bad wire; works fine until load is placed on the motor.you can get the 2 wires from autozone for less than 20$. Try it and see what happens.