Put premium in for the first time and the engine runs surges between 500-800 rpm, is this a by product of the computer learning or changing the fuel curve or a service issue?

 

mrtnt3x - I don't have issues when ideling but I posted something simular when I'm crusing and using the throutle to speed up or slow down around 30 or 40 MPH it surges trying to keep a constant speed. Read my issue - https://themustangsource.com/f726/20...3/#post6606213

 

hello all iam sure you guys are all getting sick of the same ole questions and all but a first time mustang owner here i recently bought a 1992 lx notch 5.0 man trans and supposedly it has a mild cam but cannot tell due to the ideling issues also it has headers down to x pipe into mufflers and dumps so what is happening is upon startup cold or hot does the same thing it idles from 500-1300 up and down up and down and also at low rpms it sputters and surges but if i drop down a gear and rpm's get higher then it runs ok as long as i keep the rpm's above 2000-2500 also a seperate issue the trans 2nd gear barely ever wants to stay in it always kicks itself out and 3rd gear grinds any help would be appreciated guys thank you so much!