Hi all. Lost my previous Accord in a total loss crash, and walked away so I just went and bought another.

After all the fixes, one problem remains; High fuel consumption. And it does not pass emissions due to high hydrocarbons (320 hc.ppm at idle, engine hot, and 360 at 2,500 RPM).
This high number alone tells me some sensor or injectors are to blame.
The avg. consumption is 17-18mpg.

I'm listing here some poss. root causes, but wanted to ask here before going through them as I need to save $$.
-MAF, fuel pump, injector cleaning, oxygen sensor.
The engine runs smooth at idle, but occasionally it does have that rhythmic surge problem. It has great pickup and power. No problems there.

I've fixed a few naggles, it has way more mileage than I thought. (likely rolled back, maybe has over 200,000 mi.). Here's a short list of things I've done and checked; (some by a pro mechanic at an independent shop).

New spark plugs, filter, 20-50 oil, air filter. Checked and tightened intake air resonator assembly. (it was way loose and some hoses were disconnected). Checked all vacuum hoses. New battery. Checked spark plug cables. Changed all belts incl. timing, checked PCV valve.
New exhaust pipes from the cat converter on. This alone seemed to improve power and consumption somewhat. the s4ithead who had it before did a crap job, had a narrower pipe routed on top of the suspension, and it was crimped by it!.

I'd appreciate any feedback, as the next fix, will be the last for a few months. Thanks!

 

Is Check Engine LIght (CEL) on? If yes, extract the code/s (see DIY forum for obd1 codes). Post your codes for additional help.

Some easy things to check for fuel leaks:

1) Fuel pressure regulator - Pull vacuum line and sniff for gasoline. Strong smell of gas indicates regulator diaphragm is ruptured.

2) Check fuel rail to fuel injectors for leaks - sniff, feel for cool spots. Drips are hard to detect and evaporate quickly.

3) Check fuel lines for pinhole leaks - again visual inspection and sniff are best tools.

PS I'll move this for better responses.

good luck

 

Yes there is a code 12 EGR. Forgot about that. Also I did clean the EGR passage tray. it was clogged with soot. **The code clears up by itself on the second engine start, after it has warmed up.
I suspect there's no thermostat on the cooling system since the liquid flows out from the top hose right on the first start. I'm sure this is related to the EGR code, since it works with engine temp, correct?. However let's not rule out the EGR being bad, I just don't know how to check it yet.
I have the manual on PDF and will be checking this again.

Thanks!

 

Low temperature would account for poor fuel mileage.

Where does temp gauge point when fully warmed? It should point to 3/8 to 1/2 of full range. If much lower then coolant temp may be too low. A new OEM thermostat may cure low fuel mileage.

If EGR cleaning cleared the code 12, EGR system is likely OK. EGR is usually not cause of low fuel mileage in any case.

good luck

 

UPDATE; it's been a few days, I installed a new, US made, Gates 180deg thermostat. Results;

-The code 12 EGR still comes on, but only about 1 in 3 cold starts.
-The idle hunting is still going on sporadically, independently of engine temp, it revs quickly from 800 to 1,300rpm -/+. According to forum posts, I need to clean the IACV.
What's better is that the engine reaches temp quicker, and it idles lower once the idle bouncing quiets down. It's still too early to tell if the gas consumption got better since I've idled a lot, when I finished the thermostat install etc. I will also bring it to an emissions test bench to see if there's improvement.

Lastly; I noticed cracks on the intake pipe, this I'm sure impacts idle speed as the engine is sucking more air than it should. I'll replace this with a stock used part if I can find it, or one of those placebo CAI's. lol

Any tips for the remaining issues (idle bouncing, EGR code), are appreciated!.

Thanks.

 

For the bouncing idle, check out the Common DIY and Info. Threads sticky at the top of this forum. Specifically, IACV Cleaning and FITV Cleaning.

 

Cracks in intake duct will not affect idle, but not good since unfiltered air enters engine. Suggest cleaning duct w/ alcohol and wrapping w/ radiator hose repair tape. This will form a durable, but not permanent repair.

A 180F thermostat may not hurt anything, but is below spec (195F) and may affect fuel consumption.

Idle air fluctuation is usually result of intake air leak behind throttle plate(vacuum line, PCV line, brake booster line, or intake manifold gasket leak. Try spraying throttle body cleaner around suspicious points and listening for a change in idle speed to locate leak.

good luck

 

Two changes, resulted in partial success! After the thermo change, I also adjusted the idle screw, turned it out 1.5 turns (one first, then more). I'm at a high altitude city, some 2,600ft ASL. So;

Idle is now stable, no more CEL, and altho the idle sometimes does bounce, it only does it about once every few days. Not every day as before. AND there appears to be a 10-15 % improvement in fuel economy, which was the goal of all this.

Looking at several guides of what the IACV is supposed to be doing, I can tell this is partially to blame, because the idle does not increase any, if I switch on the AC, put an electric load, put in or out of gear, turn steering wheel, etc. any of these inputs should make the IACV increase idle, but it doesn't. So, I'll just have to wait to clean the whole intake systems.

 

Further, I found this really detailed guide on troubleshooting idling problems on hondas, and have tested the IACV as explained on point :
23.5.1 To Cause the IAC Valve to Fully Close

And the idle did drop lower than it was, with the engine warm. It's a really good guide with screencaps of Honda diagnostics;

Honda IACV explained - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

 

The diagnostic page posted is directly from a Honda shop manual which it why it is so good. The first thing I would do is remove the air intake hose, start the car, spray throttle body cleaner directly onto the IACV port located inside the throttle body on the side. You will likely have to manually rev the engine to keep it from stalling while doing this. Often times doings this is enough to get the IACV working again. You may have to readjust your idle after doing this since you already adjusted it.