Engine backfires at low rpms when decelerates
 

Hi guys. I'm having some problems with my '93 FD3... when I push the throttle gently to 2000 rpms and then I remove the foot from the pedal, it backfires when decelerating, and sometimes when I start it too. I've removed the pre-cat because was damaged on the inside and it was working fine, but when I changed the spark plugs (BUR7EQP, BUR9EQP), spark plugs cables (NGK), air filter and fuel filter, it starts making this backfires... also some days ago I was cruising and the Check Engine light turned on, I stoped the car and turned back on and the light went out, but when i arrived home it was giving me a code error nº17 (O2 sensor, I believe). Is there anyone out there familiar with this problem? I apreciate any help I can get, because I'm from Portugal and these engines here are like water in the desert, there aren't anyone with knowledge, even in the oficial dealer. I was thinking in improving it's power, so I've searched in several tuning and performance shops, but they simply don´t know:scratch:... Thanks

Is it a backfire? Or more like a stumble/misfire where the car jerks a bit?

Backfires are normal, that happens when your car is running a bit rich in fuel, so when you decelerate the extra unburnt fuel is ignited by the heat.

A misfire is caused by something more serious and you can feel that when the car itself jerks for the split second.

Hi, it could be misfires as you mencioned, because the car "shakes" a bit when decreasing rpms, from 2000 rpms below (to idle)... regarding the code 17, the manual service repair mentioned 6 or 7 possibilities of causing this error, but could it be from the O2 sensor it self?
Regards

From where should I start looking for the problem?
:scratch:

My rx was doing the same thing a while back . My car had the smallest vacuum line disconnected . And that was it for me .

List your mods for further assistance.
I had these issues few months ago.

Sounds like rich fuel. If your fd has a decent street port and you're using the stock ecu, it'll do this a lot. Mine does the same, but not as much once it's warmed up.

Test the throttle position switch, I had this problem when mine was faulty