Rough Idle, Engine Light / No Code, Backfiring / Popping--Need Help!
 

I have an unusual problem that's been getting worse over the last few days...I've searched over and over since yesterday with no luck, so if you guys can help that would be greatly appreciated.

Symptoms:

1. For the last 18 months, I get the Engine Check light come on when the car really warms up, usually after a good 30 min drive. Amazingly, I can never get a code...but it hasn't bothered me much because it only makes the Fd run a little rough until it turns off again.(usually after a few minutes) Sometimes a quick blip will make it turn off when it first comes on. Somedays, it never even appears. Weird...never figured it out.

2. More serious problem. Starting 3 days ago...after a good drive for more than 30 minutes, Engine Check comes on, but this time starts to make my my idle jump up and down between 850-500 RPM all while giving out nice little popping noises from the exhaust (rich?)...when I blip the throttle it wants to turn off, but comes right back up and starts jumping again...So I start driving and it seems very unresponsive, takes a second after hitting the pedal for it to start moving and pops like crazy, even while accelerating...once I start getting over 3,000RPM, it starts to get a lot more smooth...but still backfiring/popping.

It was getting very bad at the lights, backfiring/popping, I'm giving it a little gas so it won't stall...So I pull over and turn it off, I keep the ignition and the parking lights on so the fan can turn on while I'm looking under the hood. I notice the fan come on but turn right back off in 2 seconds and come back on, it did this a few times and finally stayed on. WTF? Never noticed it do that before...

So I'm looking near the Double Throttle Actuator for loose hoses, and notice it opening and closing a couple times, then stops. Is this normal?? I fire it up after a minute and it's fine...perfect idle, I touch the throttle barely and it starts again jumping! I notice that everytime I give it gas , it wants to die. When the RPM reaches to almost 0, the Double Throttle actuator moves/closes for a second and the RPM goes up to 500 and starts jumping again. Seems like it helps out in not letting the motor stall. So I drive home, and it's rough at lower RPM's popping/backfiring, same story...?

The funny thing is that it doesn't seem like I blew the motor because this only happens after I drive more than 30 minutes when the engine gets real warm. This morning, it was PERFECT! Pulling hard, good, stable idle,etc. I drove it for a good 40 minutes!! But , I know this afternoon, when it gets warmer out, it's gonna start again. I think it might be electrical considering that the fans are behaving unusually...If anyone can point me in the right direction, that would be great.

BTW, only engine mod right now is a DP, and I changed the plugs and wires 2,000 miles ago. Thanks.

Sounds like it could be a short, but hopefully not, as that is a nightmare to chase down. If you have a friend with a PFC, plug it into your car, and check out the sensor check menu when that happens, to look for something amiss.
The popping and running rough thing sounds a good deal like a MAP sensor problem. Is that hose in good condition? Also, the 3,000 rpm smoothing out sounds a lot like a problem I once had where one of my secondary injectors wasn't firing sometimes due to the connector wiggling off the injector.
Hope that gives you a start on things to check.

Checked the Map Sensor...hoses are fine, but the small gas filter attached to it might be clogged I'm thinking, is that common? Also, is the trottle actuator supposed to be moving/working other than cold starts? I was thinking maybe it's closing the butterfly in the manifold, does that sound like it would cause this?

Thanks for the replies.

The double throttle would not cause these problems, but if it is randomly actuating, then you probably have a short. I haven't heard of that filter clogging, but you can just take it out and see.

Okay...I think it might me the Intake Thermosensor...it's probably malfunctioning when it really heats up and sending shitty signals to the computer, making it run super rich...Maybe that's why my fans are turning on and off... How does the computer turn the fans on, is it according to the signals it recieves from the thermosensor? Does the computer think there's load when there is'nt? How does it know what the temps are? Can someone please let me know if this sounds like the Intake Thermosensor? Thanks.

By the way I disconnected the Double Throttle, helped a little...but same symptoms when it heats up.

Have you checked the plugs !?
And Is the airpump running when you Idle ! ?

Yes. I changed the plugs and wires 2,000 miles ago.Checked it out to double check yeasterday. I also checked the airpump and it's running fine. And I double checked the MAP sensor, it's working.

It seems like it's a problem I had, that just got worse 3 days ago...Only happens when I drive hard and it gets very warm under the hood. Does it sound like the Air thermosensor could be it?

It could be the IAT sensor, but I'm not positive. It is really easy to test if you have an ohm meter. Why don't you just try disconnecting the sensor and seeing if anything changes? That is easy enough. It still sounds like a short to me, but since it's so easy to test the IAT sensor, try that first.

If any body comes across this thread who have the same symptoms I had...just want to let you know it was the water thermosensor. It's located behind the thermostat housing incase you didn't know.

You might want to change your thermostat as well and change your water thermoswitch with the miata one while your at it.

Thanks for all the input guys!

nice job. it is good to get closure on some probs.

I actually fixed it a while back, but forgot to mention it in the thread. I guess better late then never.

BTW, I still have the symptoms mentioned in the paragraph labeled (1) in the first post...but it's not serious and I've learned to deal with it. Hopefully one day I'll get a code out of my FD... :rolleyes:

so when the light turns on you have never jumped out of the car and ground the ten and grd connectors? or you did and nothing came up?

I guess you don't remember...let me refresh your memory. Check out the discussion we had...never came to anything solid since.

https://www.rx7club.com/showthread.p...hreadid=228218