98 Mustang GT running rough

[sanitarium16]

I have a 98 Mustang GT with 96,950 miles. It is automatic. I maintain the car meticulously. Oil used is QS Advanced 5w30....just completed an auto-rx treatment. Tranny fluid was changed a month ago.I've had a problem with my BBK Under drive pulleys causing my serpentine belt to "glaze". The belt is making a little noise. The UDP's are piggy back style.....they use the existing harmonic dampener....I dont think this could be causing the harshness but i have replacement pulleys on the way because I want a one piece design. When i first start up the car it idles rough...It never did this before...If i look under the car i hear tapping coming from the bottom of the engine and i can literally see the H-pipe rattling around (it is not loose). After about 20 seconds the tapping stops and the engine runs rough. I replaced the plugs last month and the wires about a year ago. PCV valve is also about a year old. Air filter brand new amsoil eaa..02 sensors brand new.....just cleaned throttle body and there are no vacuum leaks. Its driving me nuts. Can the pulleys or a slipping belt cause this? I think it is the wires but i dont want to spend 100 bucks for no reason. I also cleaned the idle air control motor but it is still doing it.

 

[brianl703]

Have you scanned it for codes? Are there any?

A leaking EGR valve could cause a rough idle, but there would normally be a code for excessive EGR flow if that's what's happening.

 

[Dark Jedi]

have heard about the EGR lines clogging with carbon. might want to check your lines and see if they have any build up.

 

[punisher]

Before you buy any parts, pull codes and look for any P03XX codes. I have seen bad purge valves from the EVAP system, vac leaks and ignition problems cause rough idles on those. Never have seen an EGR cause a rough idle on any 4.6 , yet, but there is a first time for everything. As brianl703 said you will get an "excessive EGR flow" code if the valve is hanging open. Pull codes and go from there.

 

[mechtech]

Take the belt off, and run it for a short while, and see if it smooths out.

 

[sanitarium16]

No codes are coming up in the computer. Bringing it in tomarrow. Let u guys know what it is.

 

[sanitarium16]

Had pulleys and belt replaced.....still have the condition a little. i have a stong feeling it is the wires..