New Member. Trying to sort out my Salvage 996

I've been lurking the site for years and have recently purchased my first 911. 2002 model with a reconstructed title. I was feeling impulsive and I liked the sellers story so I bought it. I've been using the tech articles to do some maintenance and repairs and they have proved very helpful. I'm fighting with a check engine light and an irregular idle under during specific circumstances. I'm hoping someone can point me in the right direction so I can stop throwing money at things that aren't fixing my problem. The check engine light was on when I purchased the car. The owner told me it was the air pump. I didn't give it too much thought because I was excited and intent on buying it. I drove the car for weeks and would experience an idle drop when sitting at a stop. This only occurred after a long highway jaunt or after a brisk acceleration spree. The idle would drop a few hundred RPMs then jump right back up to normal and stay solid. It was such a minor issue that I didn't let it bother me much. My attitude changed when I drove though a big puddle one day and the car started mis-firing immediately. I limped it home and started reading. I found my answer within a few minutes so I ordered new ignition coils. 5 of 6 were cracked and I was confident that would fix my engine light and idle issue. During that repair I also replaced the spark plugs and had the mufflers modified for more sound(Fister Mod). Did that fix the engine light?........ Nope, It came on a few days later(idle problem continued too) and I read the codes. Low cat efficiency on both banks. No codes for air pump like the previous owner suggested. I thought about replacing all o2 sensors at that point but I decided to take it to a Porsche shop for their diagnosis. They told me that my o2 sensors were fine and that my exhaust temps post cats were too low. Their recommendation was to replace both cats and quoted me $2200. I used this as an excuse to purchase high flow cats and I was confident my engine light would go out............. Nope, It came on a few days later. After another scan, I still have low cat efficiency on one bank(still have idle problem too) I lost confidence in that Porsche shop and turn here for advise. My guess is to replace all o2 sensors at this point. Agree? or is there something else I should be considering? I can't imagine that the throttle position sensor has anything to do with my low cat efficiency light. But could it fix my idle issue? Thanks in advance and here is a pic of the rebuilt 996.

I would have replaced the O2 sensors first. But, these O2 sensors are very expensive anyway so ... it may not matter in terms of expenses.

i just read some where that there is a reader that can tell you specifically if an O2 sensor is out. it was amid tons of reading, so i'm not sure what scanner. but I'm in the same boat. initially, i put some cheesy scanner on it. it gave me a P0430 Catalyst System Efficiency Below Threshhold (bank 2) Lol Rick 2000 Otherwise Mint 996

probably a Durametric not cheap, but gives you total control of the sensors

+1 duranetric

Hello and welcome to the forum! Please let us know if we can assist you with any part needs. I'm also attaching two helpful links. The first to our site's DIY tech articles on the 996 platform and the second one to our parts catalog for your 2002 model. 996 DIY Tech Articles 2002 Parts Catalog

Do yourself a huge favor and INVEST in the Durametric kit! Diagnostic Tool for Porsche | Durametric Brian Minson 2000 996 C4 Tip YOUTUBE SITE: https://goo.gl/ucQZnf

We just got in the Porsche Schwaben tool, very similar to the Durametric. Please let us know if you have any questions! Schwaben Pro Scan Tool for Porsche

I put in 4 new sensors. Light came back on in a few days. I should have done more research before throwing money at all the parts I replaced. The durametric scan tool might have saved me some money and this headache. The car is at the shop(different one) getting new brake fluid and a track inspection. I asked them to scan and diagnose the light while they have it.

sounds like an air-oil separator failure. See if you have vacuum in your intake manifold at idle? https://www.pelicanparts.com/techarticles/Porsche-996-997-Carrera/09-ENGINE-Air_Oil_Separator/09-ENGINE-Air_Oil_Separator.htm