The Background: I have a 1998 Prelude base, 5-speed with 140k miles that is all stock except for a CAI. I used to have an aftermarket exhaust system that consisted of a high-flow cat, 2.5" piping, Magnaflow resonator and OBX twin-loop muffler. I recently swapped an entire stock exhaust system back on the car, and since doing so this problem has started.

The Problem: When I press in the clutch (as if coming to a stop), the RPMs will drop extremely low - down to about 500 RPM, and the car will also stall out completely sometimes...I would say every 2 out of 5 times it stalls. In addition, I have also noticed that when crusing with a constant RPM below 2,500 the car will "bog" and "jerk" as if it is not running smoothly. If I am crusing with the RPM above 2,500 this problem does not happen.

Important Notes: This started happening immediately after I left the shop when I had the stock exhaust system installed. When I had my aftermarket setup this never happened. I did get a CEL from the aftermarket setup that was for a bad o2 sensor in bank 2. After I had the stock exhaust installed back on, I went to Advance Auto Parts and erased the code, and it has not come back on since. I have been driving the car for a few days now, and no other check engine light has come on.

 

Seems like you have a faulty o2 sensor. Doesn't have to be throwing a CEL for it to be bad.

 

My initial thought was that having the high-flow cat on there with my aftermarket system caused the o2 to foul out, but a few people I have talked to didn't think this would cause the problems I am experiencing.

Could that secondary o2 really effect the idle and driving of the car like it has been? My understanding is that the o2 being fouled out would cause the car to run rich, which would NOT cause it to idle low or have a loss of power... :confused:

 

Ive never heard of 02 fouling out on a honda because of a catback system. Your 02 must be bad. and make sure to reset the computer when replacing the 02, just pull the battery ground for 15 min. Also sounds like you have a bad rear engine mount since you did describe a jerking feeling

 

The secondary o2 would have gotten fouled out from the high-flow cat allowing more a/f to pass through than the stock one.

The "jerking" was meant to further describe the bogging engine and loss of power upon acceleration, not a motor-mount jerking...

 

First of all, the secondary O2 has not control over A/F mixture... it is there ONLY for emission purposes.

I would be looking into something with your idle circuit.. Clean your throttle body very good and also the IACV.

Also, have you checked your base timing w/ a timing light?

 

I finally got a CEL today - took it to Advance Auto Parts and hooked up the scanner. This is what I got:

P0171 - Bank 1 system too lean, and

P0171 - Fuel trim bank 1 pending.



On top of that, I noticed after the "running diagnostics" stage when it shows the checklist of everything the scanner read, it said that the O2 diagnostics were "incomplete."