Hello,

I am a very new owner of a beautiful 1993 fd. I love the car, but I don't know enough about it yet, so I feel quite paranoid about the problems I'm having. I have searched for and read many other posts of similar problems but the discussions have only confused me more...

Upon starting the car and idling it seems to be running a little rough. It jumps to 2500ish for 10 seconds as expected then stays around 1.1~900rpm on idle. This is fine, but I can feel the chassis shaking momentarily from time to time as the engine warms up. The shaking is similar to when a big truck passes you on a bridge. Is this normal?

To my knowledge, the car is stock except a catback exhaust, short shifter, and drop in air filter.

There's an apexi turbo timer installed on the car which supposedly shows readings of a/f and o2 voltage (probably stock o2 sensor... I'm not sure how accurate)... and it's reading a/f: 18.5-20.0 on idle (isn't this dangerously lean?!) with a o2 at: .03-.06ish. Having read some previous posts, shouldn't my a/f be around 14.7 and o2 at around .08? When cruising and feeding some gas, the a/f jumps down to around 14ish. Can someone give me some advice?

Another problem that I'm having is if i start the car then turn AC on, idle constantly cycles between 300rpm and 1000 rpm and it feels as if it's about to stall. The needle really jumps from one to the other! I think this is a known problem found on TBBs that should be fixed by Mazda for free? Is this correct?

Thank you for your time! I really appreciate it.

 

The shudder isn't normal if you can feel the whole car moving - that sounds like a bit of a misfire. However you needn't be paranoid about that too much since misfiring and stuff are dangerous when the engine is under load.

Another common sound is a "putt" sound as the car warms up. I don't know what causes it but it's common and not a problem.

Start by changing the spark plugs. That often helps a lot. (FDs need new plugs every 10-20k).

AFR readings ideally come from a wideband O2 sensor. If you're not certain what type it is, look into it because only a wideband will tell you robustly useful data.

FDs will definitely go lean at idle and on coast down - this is normal in many cases (I'm not a tuner, that's as much as I know). The danger of lean AFRs is when they are under heavy load. Detonation is not good, but it only tends to blow engines when you're working it.

Dunno that Mazda ever fixed it under warranty. TSBs are simply technical assistance for solving specific problems that get distributed to dealer service departments. There is nothing about a TSB that implies Mazda will fix it for free. Some people have had that in the past, but typically it was when cars were under warranty and/or they used that garage frequently.

After changing the plugs I would attempt the idle adjustment procedure (ref the 3rd gen faq) and see whether that helps. Do it after changing plugs. If you have an aftermarket ECU such as the PowerFC there is an idle "learn" process that you should do instead.

Dave

 

Thank you so much, Dave! I know my questions are on the newbie side of the spectrum so I'm glad you clarified everything for me. I just went out and bought spark plugs that I'll put on today. We'll see how it goes Plus I'll look into all the things you suggested. I'm pretty sure the o2 sensor is not wide-band and ecu is stock.

Cheers!
- Minh

 

I am at about 10-11 AFR under heavy load. but at curising speeds 2.5-3.5k RPM's my wideband AFR gauge is reading 16.0 AFR is this to lean even for cruising speeds?