I know this question has probably been asked a million times. However, I got nothing doing a search.

As the subj says, I'm looking at replacing my O2 sensor. The one in there now has well over 45,000 on it and the car is running rough (sputtering badly) when I start up first thing in the morning. Blipping the idle a few times gets it to settle at 750 and from then on out it's fine. During a cold start tho, it's feels like it wants to die.

My diagnosis: I'm running too rich when the motor's cold-started.

I've already adjusted the TPS with a DMM. The car runs better, but not as well as I'd like when it's cold.

I know there are wide-band and standard O2 sensors, as well as universal ones. Which to get and from where?

Thanx,

- JB

 

Univerals cost like $45 from any parts store. Get a Bosch brand one.

 

I'm pretty sure mine was well under that price from AutoZone. Might as well pick up a couple long extensions and a gorilla if you don't already have them cause those things are in there to stay if you know what I mean...

Cory

 

O2 sensor is ignored around idle RPMs.



-Ted

 

Any idea, then, why it's sputtering so bad when it's cold started? Could be a few things, I'm sure. Clogged injectors, dirty fuel or air filter(s), maybe BAC.

As you can obviously tell, I'm lost.

- JB

 

Too many things...have you adjusted the TPS?&nbsp If you got a 1986-1988 Zenki model, have you adjusted the idle mixture screw on the passenger strut tower?&nbsp Spark plugs and spark plug wires in godo shape?



-Ted

 

TPS: Yes, you helped me with that in a previous post. It's 1.003 at idle and .624 at WOT.

I've set the idle mix screw to best-idling (seat-of-my-pants).

Plugs are 5,000 miles old. Wires about 7K.

- JB

ps: could the throttlebody thermowax be an issue? I used to get the 3000 RPM rev at cold-start, but after awhile it quit doing it. Possibly sticking?

 

Your rotary should not be trying to idle at 750 rpm on a cold start. The wax pellet/fast idle cam should keep the idle to at least 1200-1500 rpm when cold. I would check the adjustment on the fast idle cam and also see it the wax pellet expands and contracts properly. Also, your Air Bypass Solenoid does not seem to be working. This is what causes your 3000 rpm idle at cold startup. Primary cause of failure for this is the water temp switch at the bottom of the radiator, driver's side. Wires tend to break off, or the switch itself goes bad. You should have no continuity on this switch when the engine is cold. Also, check the air bypass relay, this must be working to turn on the air bypass solenoid. Hope this helps!

Irv, Keith's dad

 

Thank you!

It used to do exactly what you describe, but now does not.

A few questions, ala "newby" style:

How do I check the adjustment on the fast idle cam. Such as "where is it?" for example. And how do I check the wax pellet to see if it's working? Pull it apart?

What and where is the air bypass solenoid?

If I find the water temp switch is bad, where can I get a replacement? I assume Schucks does not carry nor can order these?

I apologize for the newbie questions. This is yet another area where I have absolutely no knowledge. I know something's wrong, but I'm at a loss where to start.

You definately sound like you're on the right track here. Can you elaborate a little more?

Thanks again and please add more!

- JB

 

I found couple of NGK O2 sensors at

http://imports.racesearch.com/CGI/im...ct=Next+---%3E

which one do I get for my 90 GXL?

PS: racesearch.com carries Redline fluids and they are bit cheaper including shipping compared to other sites.

 

http://www.iluvmyrx7.com/Technical_I...nical_info.htm There is only one water temp sw on the bottom of your radiator, so once you find the one on the back left side, that it. Make sure both wires are on. Pull them off and reinstall them. Then start the car cold and see if you get the approx 3000 rpm for 17 seconds. Prior to doing that, make sure the BAC's connector is on the bac. The thernowax is on the back side of the throttle body with the fast idle screw and its cam. The throttle body should be removed to work on this.The thermowax operation can be opserved just by pouring some boiling water over its body and looking at the pistom move in and out as it heats and cools(I'm not a high tech person). You need to get the 88 manual from the site mentioned above in order to work on the car. I'll send some jpgs of the fast idle etc later after I mow the lawn.

 

Find that temp sw on your radiator and pull both bullet connectors off. Jumper a piece of wire b/t them. Start the car. If it idles at 3000rpm for 17 seconds, the sw was, is bad or the connection is no good, or the wiring to the ECU is corrupt, or the relay is bad. I'll attach some jpgs out of the book to give you a hint about where and how things work:

 

Another jpg here. Also remember that this water sw on the radiator will effect the 17 sec, 3000 rpm, start up. BUT, like the fella above said, the car should idle initally at around 1100 rpm and gradually drop down to 750. That is caused by the thermowax on the back of the throttle body. You have to remove the throttle body to check this out.

 

Again

 

Enough

 

Thanks very much. I'll check that out today and post back.

- JB

 

I bet your problem is originating at your BAC. I know mine is bad and needs replaced, and it seems that failure of this part isn't all too uncommon. It's also hell to replace, as it runs about $400 from Mazdatrix. Your best bet would be getting a used one if this were your problem. Anyway, I have similar idling problems, and this is almost positively the cause of mine, as all other possibilities have already been replaced with new parts. Good luck.

-Derek

 

are you sure that it is the o2 sensor ? do you have a constant monitor that will tell you what the codes are when you are driving ? if not do a search on constant engine monitor and install one then you will know what up with you ride. PEACE. ex...

 

Sorry, but I'm hung up on water temp sw and the 3000rpm for 17 second thing. One other thing that will make it not happen, is the neutral switch. Should have a ground at pin 1G in neutral. If the neutral switch is crummy, the ECU will think the car is in gear and negate the warmup cycle. Just more triva on the rx. Really not much to do with the start of this thread. By the way, an irregular idle can be caused by a egr valve not seating right, thereby letting too much exaust gas into the intake. Your car does have that type symptom. Could be several other things.

 

Sorry it took so long to get back. Had a road rally with some of the NW Forum guys...

I checked and sure enough, one of the contacts on the water thermo switch is busted. Gives me an excuse to do the summer flush & fill I guess.

So the Golden Guru Award goes to ...HAILERS! Thanx man.. I'd have NEVER figured that out on my own.

The idle itself is fine, I'm pretty sure my BAC is working because it will maintain idle no matter what I turn on/off electrically or turning the wheel. If the problem persists, that's the next place I'll look.

Constant engine monitor for an FC?? Never heard of it. I'll do a search sometime tho - thanx for the tip!

- JB

 

for future reference taranis:
the factory service manual is posted at fc3s.org. I find it very helpful.