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SN-95 and New Edge Mustangs
Engine Surge at Low RPM
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<blockquote data-quote="zinda" data-source="post: 15931433" data-attributes="member: 191933"><p>I had this same thing happen to me right after i bought my 2002 GT used with 70k miles, i had misleading codes for my o2 sensors, bought 2 new one and the codes increased to even more thsn there was originslly. Figured it has to be a vacuum leak, from my 40 years of dickin around with cars, (20 years were with carboraters and plenty of vacuum lines) i knew it had to be a leak. Since newer cars have so few vacuum lines now, it really makes finding the leak very simple. Theres a pvc valve on the passenger side valve cover. Positive crankcase ventelation valve, lets air travel in one direction through your motor. </p><p></p><p>Thrres a rubber hose that comes offvof your intake that creates the vacuum, check the underside of those hoses, it might be a 2 piece, mine was cracked nearly the entire length of the hose but was hidden on the bottom. I rrplaced that hose and put a new PCV valve in right away and my car ni longer ran like it had the workds biggest cam at idle. Anytime you have idle problems 90% will be vacuum leaks, 10% will be sticky throttle body valve butterfly. </p><p></p><p>So if you cant find a vacuum leak tgen remove your CAI and shoot some carb cleaner in the throtyle body and check with your finger to make sure itscopening and closing all the way. I wouldnt even start screwing around with your MAP or MAF sensors, you would have to run your car without an air filter to get it clogged up enough to alter your idle. Idle is when the least amount of air passes through it and has little affect on anything. Its job is to detect air as it passes quickly and sends a signsl to the computer which makes adjustments for optimal output in conjunction with your O2 sensors and adjusts timing with proper fuel injector flow to give max WOT (wide open throttle) output. The computer also uses cam timing sensors to make these adjustments along with a few other sensors like temp and prerecorded info from past driving habits stored in memory. If its not vacuum or sticky butterfly i will be amazed and will have to hear exactly what it is so i can be ready for the unusual and unlikely repairs i may face someday.</p><p></p><p>If it was your fuel pump or filter it would be noticable more when you give it gas not at idle since your fuel pump always has a constant pressure no matter what RPM the motor is at, thats what the return line back to your tank is for. I hope this makes sense, your fuel pump will shut off when it gets too hot and it will usually do it after its been running for a while, eventually the fuel pump motor will sieze from the heat and not be able to spin (they spin at around 10k RPM)! Keeping over a 1/4 tank of gas will help prolong the life of in tank fuel pumps, the gas cools the pumps.</p></blockquote><p></p>
[QUOTE="zinda, post: 15931433, member: 191933"] I had this same thing happen to me right after i bought my 2002 GT used with 70k miles, i had misleading codes for my o2 sensors, bought 2 new one and the codes increased to even more thsn there was originslly. Figured it has to be a vacuum leak, from my 40 years of dickin around with cars, (20 years were with carboraters and plenty of vacuum lines) i knew it had to be a leak. Since newer cars have so few vacuum lines now, it really makes finding the leak very simple. Theres a pvc valve on the passenger side valve cover. Positive crankcase ventelation valve, lets air travel in one direction through your motor. Thrres a rubber hose that comes offvof your intake that creates the vacuum, check the underside of those hoses, it might be a 2 piece, mine was cracked nearly the entire length of the hose but was hidden on the bottom. I rrplaced that hose and put a new PCV valve in right away and my car ni longer ran like it had the workds biggest cam at idle. Anytime you have idle problems 90% will be vacuum leaks, 10% will be sticky throttle body valve butterfly. So if you cant find a vacuum leak tgen remove your CAI and shoot some carb cleaner in the throtyle body and check with your finger to make sure itscopening and closing all the way. I wouldnt even start screwing around with your MAP or MAF sensors, you would have to run your car without an air filter to get it clogged up enough to alter your idle. Idle is when the least amount of air passes through it and has little affect on anything. Its job is to detect air as it passes quickly and sends a signsl to the computer which makes adjustments for optimal output in conjunction with your O2 sensors and adjusts timing with proper fuel injector flow to give max WOT (wide open throttle) output. The computer also uses cam timing sensors to make these adjustments along with a few other sensors like temp and prerecorded info from past driving habits stored in memory. If its not vacuum or sticky butterfly i will be amazed and will have to hear exactly what it is so i can be ready for the unusual and unlikely repairs i may face someday. If it was your fuel pump or filter it would be noticable more when you give it gas not at idle since your fuel pump always has a constant pressure no matter what RPM the motor is at, thats what the return line back to your tank is for. I hope this makes sense, your fuel pump will shut off when it gets too hot and it will usually do it after its been running for a while, eventually the fuel pump motor will sieze from the heat and not be able to spin (they spin at around 10k RPM)! Keeping over a 1/4 tank of gas will help prolong the life of in tank fuel pumps, the gas cools the pumps. [/QUOTE]
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