a rough idle
 

My 98 sport has a rough idle when i bought it it was alot worse the cat was clogged so i got it replaced with a magnaflow direct fit and it started running better i changed the oil and it started running even better i changed the plugs and just the plugs and now it runs worse its got a rough idle but when i start moving it runs good for a while then starts kind of chugging (just started doing this today) when i come to a stop light it idles rough if i put it in nuetral it idles better but still rough i am starting to think it could possibly be the torque converter but not sure because after a bit of research it is showing no other signs of that being the issue any other ideas? i am running NGK V-Power plugs now

What are the plugs gapped to? Is the firing order correct? Are the plug boots seated fully?


Why stop with the plugs? Replace the wires, cap and rotor, and maybe the coil while you are at it. Could even be the old o2 sensors were used to the old cat and now they cant keep up. Why was the old cat clogged? What did the plugs look like? I would check the fuel pressure to make sure it wasnt running too rich or too lean. The o2 sensors will pick up on that, and if they are failing they could have been sending bad info back to the computer which could be what killed the cat. Replacing a dead cat is easy, but you should always check the rest of it out to find out why it died, or the new cat could suffer the same. $$$


Give it a full tuneup. Check the throttle body for carbon buildup (soot). If thats dirty, the IAC probably isnt far behind. Remove both, clean both.

the plugs are gapped to .035 firing order is correct the boots are fully seated i stopped with the plugs because the wires where replaced not to long before i bought it by the previous owner and when i checked two of the plugs they where black i am not sure why the old cat was clogged and i had it replaced at a local shop