The other night in my 02 WRX I was driving until all of a sudden I got a really weird issue where the revs shot up about 750 rpm during shifts (initially thought it could've been driver error but quickly determine it wasn't). When I came to a stop and shifted into neutral, the car began idling around 2k rpm. Next day when I went to drive it the high idle and rev jump issue has dissipated for the most part however there is still an abnormal presence of rev hang (beyond usual rev hang that I have noticed after a year of driving this car) and also the revs drop slowly. It seems when I let of the gas the revs drop slowly get hung up a little around 1.2k and then goes down to idle around 750rpm.
What I have done in efforts to remedy:
Cleaned all throttle body sensor connections
replaced two split hoses (vacuum)
Any ideas on the issue I'm having here?
Car has a K&N Typhoon CAI and an Inlet. I haven't really noticed a loss of power but I've been driving out of boost since this issue has arose. Cruise Control cable looks to have a little slack but I might try loosening it up more. Car has proper oil and coolant levels. I'll post a video of the tach and a MAF sensor reading off of an OBDII reader to show what I'm talking about.
Update: So I cleaned the IACV and put a new gasket in. I should've taken before and after pics because that thing was gunked up. Car seems to run better however I'm still unsure whether it has fixed the issue. I followed a writeup on nasioc exactly. I'm going to drive it a little more to see if I still have the rev hang issue and weird idle.
So the issue still persists. It went away for a while and then all of a sudden it came back. I took it to my local subaru shaman today. The guy's awesome he's from turkey and used to race cars. Really knowledgeable and funny guy who really likes cars. He said it was likely the a IACV sensor so that is my next step in hunting down this issue.