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Hey guys I have a quick question when I'm driving my car my AFR is on point but when I'm driving the car at around 2k rpm the car goes lean all the way to 16 on the aem a/f gauge then after I pass that it goes back regular. I don't understand what could cause it to lean out every time it hits 2k-22k rpm. Your help is highly appreciated

Hello! I've got a couple of threads on here documenting my (slow) restoration and progress with my 89 Silver Conquest TSi. It was modified by the previous owner and I am trying to clean up various details and make the car reliable and streetable. Currently, I'd like to fix a lean condition the car has when it is in open loop. I think it has had this condition since I got it, but I am just now isolating it as I have made various changes (mostly to the MAF system and the cam). It idles around 16.0 to 17.0 and stays lean in acceleration and cruising until "closed loop" kicks in. When closed loop comes on, it idles and cruises around 14.7 (with rich and lean swings). If the car is warm enough for closed loop, I can disconnect the O2 sensor and it goes back to being lean, with some swings toward stoichiometric. As it warms up, with the O2 sensor disconnected, it does seem to swing more from lean to occasionally stoich and even slightly rich. Also as it warms up, but before closed loop, it seems to be lean around 15.5 to 16.0. On a cold start, it stays mostly at 16.0+ when you first start it. Some of the things the previous owner did related to this : 1) Replaced all vacuum lines (I haven't checked the lines that lead inside the car, though) Some of the things I have done recently : 1) TPS/ISC reset (many times) 2) TPS sweep test (always fine) 3) New BUR7EA11 plugs 4) New NGK (part 8079) wires 5) New distributor cap and rotor 6) Reset timing 7) Set idle at 900 rpm 8) Cleaned up the main four fusible links and the negative ground nearest the battery. I do still have some grounds I could clean around the engine compartment. 9) Put a little LED light on the glovebox code readout. It doesn't show any codes, except the O2 sensor until closed loop. Some of the things a friend and I did today : 1) Replaced the CTS with a known good one 2) Replaced the PCV valve with a known good one 3) Replaced the MAF with a known good one (went back to my MAF when it didn't stop the lean condition - and I've put two different MAFs on) 4) Capped off various vacuum lines, plus the line to the PCV valve, to see if we could get the lean to go away. It didn't. My friend did some spraying of carburetor cleaner on my intercooler hoses. That didn't seem to make the idle run any faster, so they seem to be okay. I think it could still be a vacuum leak, but I don't really want to spray carb cleaner everywhere. If the consensus here seems to be that I still need to track down a vacuum leak, I will get a little propane torch and some tubing and use that. The reading I have done keeps pointing to a vacuum leak, but another thing that causes me to wonder is that I have an aftermarket boost gauge which shows the vacuum to be around 18 inches or so at idle. That seems to point away from a vacuum leak. I made a video tonight that shows the car on a cold-ish start. I video'd the AFR, the code LED and the boost/vacuum gauge. You can see in the video that it mostly stays around 16.0+ AFR, but it occasionally spikes up to 14.7 for just a second. No LED code lights beyond the O2 warming up. The vacuum on the boost gauge reads around 18. I am getting a bit frustrated, although I will stick with this. I'd appreciate any thoughts anyone has. PS - Mods in signature...