Adam Holland

Hi all, I'm having an issue with my friends 07 mazda 3 with the 2.0 @ 150k that I'm helping him with. When I got the car, it would idle hard when warm and ran p0300 and p0171 codes. Some research showed that the mass air flow sensor could cause problems, tried cleaning the old and installing one new, no change in symptoms. Further reading showed that the EGR could stick and cause idle issues, I removed the EGR and cleaned it thoroughly, no dice. In the process I removed the throttle body, cleaned it up (very greasy and dirty) and replaced the throttle gasket. Car still runs rough. Using the carb clean technique I looked for any vacuum leaks, but couldn't find any. Resorted to inspecting each vac line, esp the rubber hose to air box, everything looks ok. Tried a known good battery for the hell of it, no change. Air filter is also clean. Put some fuel cleaner in it as well, no difference. The plugs are all good (iridiums, I put them in last year). Is there anything I'm missing? I've heard that the intake mani gaskets can be an issue as the plastic manifold can warp. But, spraying carb cleaner liberally on all gasket areas I get no change in idle. When rechecking the codes, I got a p2274 (iirc) which is for the third sensor. Usually the downstream sensor only monitors the cat efficiency, but since it was the first code on the list (usually organized by priority, afaik) we tried a new sensor. Now, the car runs even worse. It is the correct sensor, denso 234-4329 (Ca emissions). It runs so rough, it can't be driven, because the vacuum brake assist (I am assuming) is so weak the brake booster can't function. Throughout this whole process, the car would run ok when under power, but would idle rough. Now, it revs up fine, but idles horribly and can't be driven because the brakes have no power. What's even more confusing is that even though the car feels like it's about to die, there are no check engine codes. I work on all my own cars and do jobs for my friends, but at this point I am ready to throw in the towel. Is there anything else I can try? I would like to test fuel pressure, but I don't have an adaptor that can fit onto the quick release lines. I've pulled each injector to look for a change in idle, no change.

last codes I had were: bank 1 too lean o2 #3 stuck, random misfire, system lean
-Tried new MAF
-Checked all plugs
-Looked for vac leaks
-Tried pulling individual injectors
-Cleaned EGR, plunger moves smoothly
-Cleaned throttle body
-Tried good battery
-New downstream sensor

edit: should add that I swear I can hear a vacuum leak. Initially, the car would run rough when cold, and seemed to hiss. After I would rev it up, I would hear the hissing stop and the idle would improve. Now, the hiss is always there and the idle is bad no matter what.