Hi everyone, my 04 honda accord auto, 2.4 has a Rough Idle after warming up. At a red light, ect if i let off on the brake a little i can feel it like "chugging" dosent stall, but if i turn on the heat or say headlights it seems to get worse. i got a P0171 code a couple of times eariler in the year when it was really cold outside, but it has not come back on since. My idle has gotten worse while in drive/reverse. but normal in neutral..

 

P0171 is a fuel system too lean. Even though code may be off, the system may be running lean. This code is frequently caused by an intake air leak (intake manifold gasket, vacuum line leak). It can also result from a partially blocked fuel injector.

An obd2 scanner w/ data monitoring capability will show if Long Term Fuel Trim (LTFT) is excessively positive (perhaps > 10%). If LTFT gets up to about 15-20 % code (P0171) is likely.

Some diagnostics are in order to determine intake air leak or fuel injector.

Intake air leaks can be detected by observation or using a smoke generator. I've used a cigar rigged to inject smoke into vacuum line while blocking intake w/ rubber glove. Check scottykilmer channel on youtube.

Fuel injector blockage requires a special tool to perform a pressure loss measurement while pulsing the injector open/closed rapidly. Pressure losses should be almost exactly same for all 4 injectors. Check scannerdanner channel on youtube if you want to DIY. I had this test performed by a shop to confirm a partially blocked injector was causing P0171 on a toyota celica.

good luck

 

Well, today the problem seems to still persist. I checked for vacuum leaks with a propane torch on all available areas, no change in idle. Replaced the PCV valve, it was pretty dirty and noticed some oil on the head threads. The spring inside diddnt look right from the top view either. Replaced the MAF sensor as the honda dealer suggested, waste of money. Still no CEL but the Idle is horrible in drive or reverse. Should i go for the O2 sensor up-stream or IAC? Original code when the CEL light was on was PO171. Or just bring it to the honda dealer and have them charge me $112 to hook it up to their scanner? I cant think what else it would be. 04 honda accord ex, auto 4 cycl, SULVE system.

 

Your engine likely uses an Air/Fuel sensor which costs more than an O2 sensor.


Idle speed problems are usually caused by dirty idle air control valve and throttle plate. If engine is missing at idle something else may be wrong.


W/O some diagnostics, it can get expensive to find problem by part replacement. A good obd2 scanner can be purchased for < $100 these days. Check amazon.


good luck