Hey stoneage I posted on here a few days back about my deville's rough idle,but seeing what it did this morning I think a more accurate term would be that it is stuttering when idleing. By stuttering I mean what it does is after being started is it idles but seems like it wants to cut out but dosen't. Now being its got a complete tune up,the egr tubes and throttle body has been cleaned a few months back,fresh oil and new fuel filter my first thought as the culprit is my fuel pump which is dying.

Does this mean the fuel pump is getting worse,is this one of the symptoms of a dying fuel pump? I really need your advice stoneage as I'am pretty much stumped as to what could be causing this,I'am really worried its something major like a timing chain,although I'am praying its not. Last thing is I've been forced as of late to put 89 unleaded in it a few times as thats all the gas stations that actually had gas had left. Could this be the cause of my problem?,and whats the worse that can happen from using gas under premium grade in these 4.9liter engines? I always as a general rule use 93 unleaded but was just wondering why these cars call for premium unleaded fuel only?

The 4.9 does not have a spark knock detector so it is not very tolerant of 87 octane, however, that should not be a problem at idle. How about the plugs, wires, distributor cap and rotor? Have you replaced any of these components or cleaned any of the contacts? What is your fuel pressure? Have you checked it?

Ranger the cap,rotor and distributor are all new anf the connectiona are clean. I haven't checked the fuel preasure but when my fuel gets below half a tank the car sputters like its not getting any fuel some here have said its an overheating fuel pump.,could this be causiing my stuttering at idle? How do I check the fuel preasure,and woulden't a fuel preasure issue be apparent no matter how much gas was in my tank?

get a fuel pressure gauge fromt he local autoparts store and find a way to have it hooked up tot he schrader valve ont he fuel raila nd still be able to watch it as you drive the car , you need to be over 40 psi prolly more i cant remeber what the specs are ....

Thanks stoneage and ranger as far as my fuel situation when the tank get below half a tank and the car sputters,is this the fuel pump? Or could it be caused by a fuel preasure problem? I'll have the fuel preasure checked and report back but was just wondering if a fuel preasure issue would be a constant thing or would it only show itself when the gas got below a certain level in the tank? Should I still replace my fuel pump this month? I don't want to spend $300 for a new fuel pump if this isn't going to fix my problem of the car running like crap if it has less than 10 gallons of gas in the tank thanks.