Mines currently doing the same thing. 1998 Mustang GT, idles fine on start up and the first few minutes of driving. After a while, when I come to a stop the idle raises to 1.5k rpms. It would drop down very slowly but only to 900 rpms then slowly creep back up to 1.5k. Has a brand new fuel pump.
If you didn’t get it fixed, my guess is that it might be throttle/throttle cable because if you had already taken it out and came back it could’ve just gotten slightly hung up at some point on your drive. I don’t know for sure but just my two cents😂
Does your car idle better if you unplug your iac? Mine is revving at 2k rpm at idle unless i unplug my iac whil the engine is running it lowers the rpm to about 700-800 my guess is we have bad iac valves, i had a friend who asked me to clean his iac or egr every couple of weeks and im guessing after a while cleaning them only fixes the issue for so long, I havent tried cleaning my iac yet not trying to if i sont have to either because i heard you have to make the car relearn the idle and im already having a handful trying to fix this issue
If I unplugged the IAC the car would die almost immediately. I swapped two different IAC valves and didn't make any difference. The problem ended up being my fuel pump
@@jfisher99999 i recently had to replace my fuel pump as well turns out i was forcing it to see its last days in retrospect the cleaning the iac did little to nothing compared to when i had a new fuel pump
Have still yet to figure it out. I hooked up a smoke machine to it and am not seeing any smoke besides from the little IAC cap. No noticeable hesitation off idle. I am going to pull the intake mani and delete the IMRC's and do an intake valve cleaning. After that it's going to Lee Blankenship for a tune and to see if he see's anything obvious
@@jfisher99999 right on let me know cause I have the same issue. I’m thinking something in tune and I’m about to take my intake off and clean imrc also. Keep in touch!!
@@rowdyray44 my issue ended up being the fuel pump. It had an aftermarket pump in the car that wasn't a variable voltage pump (98 and newer have variable voltage pumps)
yep, it ended up being my fuel pump. I knew I had an issue with fuel as my car would cut out completely going around turns and the car constantly trying to add fuel at idle. Turns out the car had an aftermarket 340lph non variable voltage pump that I think was on it's way out. Swapped out the pump and it took some run time but eventually started idling perfect
ended up being the fuel pump on it's way out. It's a 98 so it has that variable voltage fuel pump stuff. Previous owner installed a regular non variable voltage fuel pump in car and it was dying
Mines currently doing the same thing. 1998 Mustang GT, idles fine on start up and the first few minutes of driving. After a while, when I come to a stop the idle raises to 1.5k rpms. It would drop down very slowly but only to 900 rpms then slowly creep back up to 1.5k. Has a brand new fuel pump.
If you didn’t get it fixed, my guess is that it might be throttle/throttle cable because if you had already taken it out and came back it could’ve just gotten slightly hung up at some point on your drive. I don’t know for sure but just my two cents😂
Does your car idle better if you unplug your iac? Mine is revving at 2k rpm at idle unless i unplug my iac whil the engine is running it lowers the rpm to about 700-800 my guess is we have bad iac valves, i had a friend who asked me to clean his iac or egr every couple of weeks and im guessing after a while cleaning them only fixes the issue for so long, I havent tried cleaning my iac yet not trying to if i sont have to either because i heard you have to make the car relearn the idle and im already having a handful trying to fix this issue
If I unplugged the IAC the car would die almost immediately. I swapped two different IAC valves and didn't make any difference. The problem ended up being my fuel pump
@@jfisher99999 i recently had to replace my fuel pump as well turns out i was forcing it to see its last days in retrospect the cleaning the iac did little to nothing compared to when i had a new fuel pump
Did you ever figure it out? And does it have a hesitation off idle? Mine is doing the same thing.
Have still yet to figure it out. I hooked up a smoke machine to it and am not seeing any smoke besides from the little IAC cap. No noticeable hesitation off idle. I am going to pull the intake mani and delete the IMRC's and do an intake valve cleaning. After that it's going to Lee Blankenship for a tune and to see if he see's anything obvious
@@jfisher99999 right on let me know cause I have the same issue. I’m thinking something in tune and I’m about to take my intake off and clean imrc also. Keep in touch!!
@@scottlatinette4374 I have a 97 and having the same issue currently. Some time has passed were either of you able to find the cause?
@@rowdyray44 my issue ended up being the fuel pump. It had an aftermarket pump in the car that wasn't a variable voltage pump (98 and newer have variable voltage pumps)
Ever figured out the issue my cobra doing the same
yep, it ended up being my fuel pump. I knew I had an issue with fuel as my car would cut out completely going around turns and the car constantly trying to add fuel at idle. Turns out the car had an aftermarket 340lph non variable voltage pump that I think was on it's way out. Swapped out the pump and it took some run time but eventually started idling perfect
What kind of pump you put on
Replace iac sensor
Tried 3 of them. Ended up being a vacuum leak around the intake manifold adapter plate
IAC needs to relearn. Google the procedure.
ended up being the fuel pump on it's way out. It's a 98 so it has that variable voltage fuel pump stuff. Previous owner installed a regular non variable voltage fuel pump in car and it was dying
@jfisher99999 oh man. I changed mine years ago too. 340 aem. Hopefully it's not that.
I have the same issue. The car just stalls out of nowhere.
@@ivmo71 do you have a 98?
@@jfisher99999 96 cobra
maybe it just needs an ls swap
hard pass lol
The purists get so mad. Haha
with these older SN95's, the sound is really what people love about them, since they're not all that fast. An LS swap would ruin that.