12a_Mainer

Hello all! I'm new to the forum, but not so new to rotaries. I grew up with an rx7 in the household (well, in the garage...but you get the point) and now I have two of my own - a 1985 GS, 12a, practically stock with just over 70k, and a 1983 GS, 12a as well, but far less stock (rebuilt nikki, headers, straightpipe, rats nest delete, etc. I've managed to get along well with these cars without needed to join a forum thus far, but I'm a bit stumped today. So this is my welcome post, and my plea for help


Here's the deal. The '85 is legal for the road now, and is mostly running fine. I'm having an idle issue however. The symptoms are - car starts and runs fine, hot or cold. After warming up the engine (no choke cable connected) I can let it idle on it's own. However, it will only idle smoothly for about 1 minute before it starts to drop in rpm and bog/hesitate/miss.


After days of researching, I was pretty certain it was the shutter valve. When I had access to the car, attempted to diagnose the potentially failed shutter valve per the instructions on MazdaTrix. I pulled the cover off of the breather case and I plugged the hole for the shutter valve (pointed to in the pic below,) with my thumb. At idle, I didn't seem to feel any vacuum being pulled after holding my thumb over the hole and then removing it. The Mazdatrix tutorial indicated that presence of a vacuum from this hole at idle meant a faulty shutter valve. I cannot see the arm on the valve with the nest intact, but it doesn't appear to be moving. Yet, plugging the hole shown in this pic, which leads to the large vacuum line going to the shutter valve, doesn't seem to remedy my idle issue at all either.


Pic from Mazdatrix showing a pointer indicating the hole that I plugged to check for vacuum at idle (Mazdatrix indicates that a vacuum at idle from this hole likely means a faulty shutter valve.) . I felt no vacuum from this hole at idle.



I adjusted my idle speed screw, increasing the idle speed just slightly as well as decreasing it. Neither seemed to resolve the issue, so I left it just slightly higher than it was initially, to aid me in my single-person testing. It's set at about 850/900rpm now. It idles a little smoother, but after letting it idle for a minute or so, the car still starts to bog down and miss, like it's going to stall. It won't stall, as much as it sounds like it's just about to. A little blip from the throttle doesn't do much, but bringing the engine speed up to around 2k rpm and then letting off of the throttle seems to allow it to return to a smooth idle for about a minute, before it starts to bog down again.


Here are two videos. The first shows the typical duck/goose/honking noise from the breather on decel, that is synonymous with a faulty shutter valve. The second shows the car idling, after being warmed up and driven for about 10 minutes. You can see that it idles fine, for about a minute before getting wonky. If I rev it up to 2k or so quickly, it will return to a normal idle again but just for about 1 minute before going wonky once more. It won't die, but it doesn't idle properly.





I would think this is a faulty shutter valve, but the test of checking for vacuum at idle didn't really reassure me. Further, I disconnected the small vac line going to the shutter valve from the solenoid, and I plugged the hole at the breather end of the large tube coming from the shutter valve, and it still idles poorly.


I'm hoping I'm just misunderstanding something, but I'm open to further trouble shooting. The car and all will be coming off for a rebuild sooner than later, but I'd like to get it a little more drivable to get it to the garage where I can work on it more easily.


TL/DR - 85 12a rx7, stock. Idles alright after letting off throttle, but after idling for ~1 minute, it starts to idle rough. Acts like symptoms described of a faulty shutter valve, even has the "honking" sound from the breather on decel...but I am not certain.

t_g_farrell

iTrader: (1)

Vacuum leak or fuel starvation. Have you changed the fuel filter lately? How often is this driven? How long has it sat?

Make sure when it starts bogging and missing that the float levels are both still at the midpoint in the float inspection window.