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This car, 2001 Mazda Millenia 2.5L, has been troubling me with a seeming hard to resolve issue… seems that the VRIS system may be involved, but I cannot see how as these valves are only ativated at 3500 and 4500 RPMs.
From time to time they may show up as pending faults, but the problem occurs well below 3500 RPMs and I have tested the 2 vacuum pumps and the 2 valves and they are within spec. (I also inspected the lines it uses and changed a bad T connector.)
The problem that happens is that.. the engine will all of a sudden drop rpm to 0 and pop back up to where its idling (which is between 11 and 15 hundred)… It should only be around 8, but the rpms being up could be due to the electrical load on the system at the time … the occurrence seems to coincide with when the engine gets really hot and the system has kicked on the cooing fan and has cooled off enough for it to kick off… (just to be clear… the problem occurs just after the fan has kicked off.
The behavior made me suspicious of the IAC, so I unplugged it altogether and have not seen any difference in the behavior problem.
I have spent a lot of time troubleshooting this and have cleaned out the throttle body, the IAC, the EGR and the MAF… and I have tested them all as well… (I even checked the TPS and found no trouble there…. (also I verified operation of every relay I could find)
Now I have been disconnecting as much as I can to try and see if anything causes any change in the trouble behavior and so far nothing…. I have disconnected the egr vac line and unplugged the VRIS parts and disconnect the IAC and the problem occurs the same exact way that it did before… So I am having a huge problem finding a correlation and I am running out of ideas…
Saturday I bled the cooling system just to be sure and after that nothing had changed…. anyone have any ideas on this….? you can see the problem at the link below as seen from the dash… I don’t yet have one as observed from under the hood… but in a nutshell… the needle dropping an rising coincides with hearing the relay for the cooling fan kick off and then a rise in rpm sound … then a fast drop … and a rise and another drop… sometimes it can happen once… and sometimes many times in a row…(hopefully knowing that helps when you see the video from the dashboard viewpoint. Thanks anyone for any information.
Matt M
(here is a link to show the problem: https://youtu.be/PtZ0AjlNVDw)
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You might try to clean the injectors. Seem a lost of power only in low rpm. You need a special tool to clean correctly the injectors.
I wanted to post a follow up to this in case anyone else was looking at this problem.
I eventually brought this car to a shop. (Originally I wanted to avoid this because I did not want to have an expensive parts swapping session.)
The shop changed the distributor and replaced the egr valve and also replaced to two VRIS vacuum switches. … with all these parts being exceptionally expensive, the cost was over 1k.
After taking the car, I was pleased to see that the idle was now normal when warm …. but I was no more than 5 miles from the shop when the engine did a quick series of say 3 or 4 rpm “surges”… say about 2 or 3 hundred higher than it should be… and then returned to normal….
It did this a couple more times on the ride home…. I brought the car back to the shop and they had it for another week or so and when I picked it up that time, what they had done was removed the IAC and tried to clean and lubricate it…
No more than a mile into the ride home the problem recurred… and continues to recur periodically… sometimes throwing codes and sometimes not…..
Sometimes it throws a code and then the problem happens again and the engine light then goes off…. and other times the problem happens and it will flash or turn on the “hold” light on the dash (as if I had pressed the button on the shifter to take overdrive off)…
I have not been quick to say that this is just a back computer causing this… and I am still not totally in belief of that, but finding this issue seems to have become impossible….
And this has nothing to do with the shop guys…. it was evaluated by 2 ACE mechanics….
At this point I am practically resolved to just “living with it” as I don’t want to take it back to the shop and hear that they changed the IAC… that part is about 450 …. and who knows if that will be the final thing to solve the issue.
Unfortunately the biggest lesson I have learned in this is stay away from Mazda….
Thanks for listening
you know…. its funny… because I cant always get the codes because sometimes by the time I stop driving the engine light will go off….. but I managed to get it this time and the codes I pulled were P0750, P0755, P0760 and P1743. Which seems to be indicating shift solenoids a, b and c and the torque converter clutch. Also, when driving it this weekend… besides the “hold” symbol popping up on the dash it also threw the TCS and TCC light up too… but they all went away after turning the car off and on…. so that would seem to be consistent so I feel more secure that the computer itself is responding properly…. but 3 solenoids and the torque converter seems like a lot to happen at once… and the malfunction only lasts for under a minute usually and then the driving is normal……. seems like the culprit may be some sort of wiring short…. but the problem is that if inside the transmission, its a real bitch….not that I have any idea if it is or it isn’t… just happened to view a video on shift solenoids, but otherwise my knowledge in this area is quite limited
Take my point of view for what it is worth but that looks like your ECM is failing or it’s power/grounds are being disrupted. I do not think you’re experiencing a misfire or an engine drivability fault caused by a bad sensor or IAC. That check engine light shouldn’t be turning on and off like that if your ECM was working properly.
Have you tried cleaning the ground points for the engine and the ECM? Also, maybe probe the ECM power wires with a test light and watch for flickering. You should have constant ~+12V input and ~+5V output for sensor power.
my apologies for not seeing those last 2 replies… somehow I never got notified in my email…. I just happened to be coming back to give an update on this and a final resolution. I brought the car to a mechanic I know… 2 or 3 ACE certified guys… In pulling the codes and checking the symptoms, the computer software he uses was saying distributor related… swapped distributor… problem seemed to go away and then came back a couple weeks later… swapped it again… same thing…. one more time… problem remained… bottom line was that it was in fact the distributor… but the problem persisted until he used an OEM distributor…. car just wasnt able to be happy with the aftermarket ones.
Been driving the car for 3 or 4 weeks now and thankfully have not seen the problem resurface… so wanted to pass it on that the final resolution was that it had to be given an OEM replacement distributor. Thanks all for the help along the way…
Matt M
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