Poor idle, engine misfire on 84 12A
 

Thanks to all for reading and responding. I have an 84 GSL 12A with 158000 miles. Car started and ran fine on my trip to work, but when I arrived it would hardly idle and is missing very bad. It starts and runs with a terrible miss and sounds like it is running on one rotor. The car seems to run fine above 3500 rpms, but terrilble below that. The car has run fine before this problem. Oil pressure, volts, and temp gauges all read normal. I have changed the spark plugs, distributor cap and rotor with new parts. Timming is on for both leading and trailing. I replaced the following with used parts removed from a running car: complete distributor including ignitors, both coils, and spark plug wires. None othe parts have made an inprovement in the miss. I am at my wits end and could sure use any help anybody could offer. Thanks

check for vaccum leaks

maby the shutter valve? try removing the top of the air cleaner and pluging the big hole in the back drivers side. :)

Im not usre what hole your talking about. The largest hole in the air cleaner seems to run to the air pump? Anyway, I plugged all four holes in the air cleaner (one big, three small) one at a time and it made no difference. Thanks for the help. It is appreciated.

Bump to the top. Anybody ever have a problem like this?

Do you hear a wierd honking sort of noise coming from the air cleaner area?

Could you describe this noise that you mentioned further. When would you hear this noise? The engine is shaking badly at idle and almost dies. I will listen for any noise at the air cleaner. What would this noise indicate?

It is a sucking or weird honking noise from the air cleaner. If you have this noise the shutter valve is bad and would be a large vacuum leak causing your symptons. This is a very common problem.
Do a search with the term shutter valve and you will see more detailed information on this common problem.

I had a similar running problem. Had a blown engine fuse. Ended up having a wire shorted to the back of the alt. Repaired rubbed wire and installed new fuse. Hope your's ends up being as easy a fix.

Check the wiring going from your coils to the ignitors. Sounds like you are running on one rotor as you stated.

Pull all 4 plugs and check for spark. I had this same problem with my car went through 2 sets of ignitors... ended up having 2/4 bad...however it was one out of each set...

Be carefull when you check for spark as you can blow out the ignitors. Don't just pull the wire off the top of the cap it will cause arc'ing... Your best bet is too pull the plugs out and check.

^ reread his 1st post. :-)
He has checked timing both leading and trailing which means no ignitor problem.

And with a timing light you don't need to pull the plugs to check them for fire. You attach and read with the light and each plug while it is running.

Yes, he mentioned that the timing was correct. However, it sure does sound like he lost his leading ignition.... Could be worth rechecking for spark on the leading just to be sure I think...

i agree it sounds like a shutter valve to me. mine lost a lot of power and felt like it was running on one rotor when mine went, also had the symptoms clear at a higher idle.

If the large hose that runs from the anti-afterburn valve to the backside of the intake manifold were leaking you could experience these symptons.

Thanks to all for the replies. I am just came in from replacing the shutter valve. I am sad to say that two and a half hours and $260.00 later, I still have the same problem. I checked the fuses and they are not blown. Would a bad alternator cause this problem? I cant seem to find any disconected hose. There are so many solenoids and valves on this car. Could any of them be bad and cause this problem? I am really bummed. I hope you all can help me figure this out becuase this GSL is "cherry" and I really want to get her going again. Thanks

I'm sorry that you spent all of that money and it did not fix the problem.
u would of checked the shutter valve before you would of found out that it was not bad.

Next thing to check is that anti-afterburner hose that sctty has mentioned. Take it off and see if there is a hole in it.

An altitude compensator valve is attached to the 1981-1985 RX-7 carburetor to supply additional air into the carburetor at high altitudes (between 1640-4920 ft.) in order to lean the mixture for better driveability. If the altitude compensator remains open at low altitudes, the following driveability problems may occur:

^ Lack of acceleration, hesitation on acceleration
^ No power under load
^ Engine stumble, surge or bucking below approximately 3000 rpm
^ Rough idle


If the above driveability problems are encountered in RX-7 (12A), always check the altitude compensator as shown below before repairing the carburetor.

PARTS INFORMATION

PART NUMBER DESCRIPTION APPLIED MODEL

N249 20 770 Altitude Compensator Valve 1981-1985 RX-7
Altitude Compensator Valve





CHECKING PROCEDURE

1. Remove the altitude compensator valve.
2. Blow through the valve from port A andB. Check that:

^ Above 4920 feet - air into port A exits from port D and air into port B exits from port C.
^ Below 1640 feet - air does not pass. If not, replace the altitude compensator valve.

NOTE:
The operating specification of the altitude compensator valve will vary between 1640-4920 feet depending on atmospheric pressure.

Thank you RX-7 doctor and all others that have replied. I did test the shutter valve and found suction in the air cleaner. After removing the shutter valve I found that the arm that opens and closes would not move as free as the new one would. The car does idle a tiny bit smoother now with the new shutter valve. I cant seem to find the anti-afterburner hose that was mentioned. Does any body have a picture of where it is located? My home is a 5650 feet in elevation. I dont know the altitiude compensator mentioned would give the problems associated with low elevation use. I only go up in elevation from my home. By the way I am located in New Mexico. Is anybody on here from New Mexico or know of a good RX-7 mechanic here? I find that most mechanics wont touch an RX-7. Thanks

The hose runs from the back of the intake manifold near the firewall.
Download a copy of the factory service manual member trochoid profile. Any member that plans on working on their 7 need to have the FSM for reference. All of the illustrations and diagnosis procedures from the factory are in there.

I found the large hose and removed it. It is a little heat cooked on the bottom but does not have any holes. I will order a replacement hose from the dealer. Any other ideas? Thanks

Does anybody have any suggestions on what could be causing my problem?

Please, any other ideas? I'm pulling my hair out trying to figure this out. Thanks!

Pull out a leading spark plug and check for spark. Let's get that out of the way first...

Thanks for the reply. I have spark on all four spark plugs.

I had the same problem on one of my race cars (with original 12A engine).

After a couple of laps, the engine was broken.
In fact an apex seal was broken and damaged the rear housing.

You should remove the exhaust system and check the apex seals this works well with a mirror without removing the entire engine.

Sorry for the bad news.
Hope I am wrong.