Background: Code 16, CEL on, I couldn’t clean the EGR valve because of difficult access to it. Idle is steady at ~700 rpms; now and then I hear backfires but nevertheless very poor gas mileage. So…
-Upon closer inspection, both ports of the 2-ported EGR valve solenoid were broken (maybe originally were, or any of the two technicians who shied away from fixing my car broke the ports). Any way, I replaced the solenoid with Mazda 626 one from the junkyard. But to no avail, Code 16 and CEL-on were still flashing on my dash. Interestingly, my sunroof stopped working.
-After acquainting myself with the anatomy of the EGR system and having the air intake in place + all hoses connected, I repeated EGR valve test:
I just disconnected the hose that communicates the EGR valve with the 3-ported EGR vacuum solenoid and attached it to a manual vacuum pump (to the EGR valve side). I started the car, let it reach normal temperature, and I created a vacuum of about 5.0 inches Hg with the purpose to open the EGR valve and cause recirculation of exhaust gases. Immediately, the idle became rough, indicating that the EGR valve might be O.K. because now exhaust gases were being ‘recirculated’ into the engine. So I assumed the EGR valve is OK and rather began troubleshooting a possible vacuum misconnection/leak upstream of this point.
-I checked all the vacuum connections, hoses and compared against the vacuum charts available in this great forum. Everything seems correct, with the following exception. Please refer to the picture attached, which most of it isn’t mine but I just use it here for illustrative purposes.
-In my car, vacuum port (labeled by me as #14 on the passanger side of the VRIS#2) doesn’t not hold vacuum when applied externally, nor it has vacuum when idling. If it were clogged, it should hold vacuum, right? So it must be leaky. So I plugged it, but still code 16 remained on. So I decided to bring an alternative source of vacuum using an unused port here labeled as # 2 beside the VRIS#1 actuator (normally should be plugged -with a mini-condom as somebody else said in another thread). This port has vacuum in the normal range (i.e., sucks real good). I’ve driven about 25 miles so far, and the CEL came on just for a few seconds, but most of the time has been OFF. Interestingly, my sunroof is working back again. Thus, it seems that I just achieved a temporary solution by bringing a strong source of vacuum, that probably works only at mid- or closed-throttle, failing at WOT (wide open throttle). In addition, I seem to hear a hissing sound from the intake manifold which I think locates to the spark boots/intake runners toward the firewall (locations ocho / nueve spraying throttle body cleaner in different spots clockwise from the throttle body. Please take a look at my video). Also I tried blowing air using a dust remover to see if was any displacement of some soap/foam I applied, but was inconclusive. It may take some time for the movie to be available, so in the meantime use as key words 'vacuum leak'..
YouTube - Diagnosing a vacuum leak in intake manifold
My interpretation is that I might have a broken vacuum chamber or vacuum reservoir, thus explaining why vacuum port #14 neither provides vacuum nor it holds it. Bringing another vacuum source like from port #1 is only temporary.
Another thing. I noticed that there’s an empty corner toward the passanger side of the engine, as if someone had removed something. Ford probes have a vacuum chamber-like box, possibly related to the HVAC, but I’m not sure. Could the previous owner removed what was there? If something should go there in the Mazda’s, then how would that affect the vacuum? Many thanks, regards, Robueno.