98 GT 4.6L SOHC Rough Idle/ Misfire (Vacuum Leak) Help Please.

amgdorsey

New Member
Apr 26, 2018
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Grand forks ND
Hi guys, first post. I have a 1998 Mustang GT (117,000 Miles) with a rough idle and misfire at low RPM's. I either cant hear it at high RPM's, or the misfire doesn't occur. The engine also shudders during idle.
- I cleaned the MAF
- Replaced PCV Valve
- I can hear each one of the injectors clicking using a mechanic's stethoscope, ( could be a bad spray pattern still?)
- Pulled a few spark plugs, looked Ok not great, maybe a bit of ash deposit but thats it.
- Could be bad spark plug wires.
- Then I scanned it with OBD Tool, Got codes PO171 and PO174, running too lean.
So thats why im thinking its a vacuum leak, what other things could it possibly be? And if you guys think its a vacuum leak where could it be coming from. Im hoping its not the intake gasket.
Any suggestions are appreciated!
 
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amgdorsey

New Member
Apr 26, 2018
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Grand forks ND
Pretty sure its not a vacuum leak now. I hooked up a code reader and looked at the fuel trims and they got much higher as I increased RPMs, it should be the opposite for vacuum leak.
 

wmburns

SN Certified Technician
Aug 14, 2009
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Houston Texas
Pretty sure its not a vacuum leak now. I hooked up a code reader and looked at the fuel trims and they got much higher as I increased RPMs, it should be the opposite for vacuum leak.
What has been done to rule out low fuel pressure and/or clogged injectors?

I have had great luck with injector cleaning and flow testing service InjectorRX.com. Once cleaned and tested they are as good as new but cheaper.