QuestionQUESTION: Hi Travis - 93 honda accord, 4 dr sedan, AT, 4 cyl. Currently the car surges from 800 to about 1400 after warm and sitting in park, idle. No surge in drive. Background included I previously had a bad hesitation in the 1500 to 2500 rpm range while driving and accelerating and seemed like running on 3 cylinders. There were egr and o2 sensor codes affiliated with the check engine light. I had a technician diagnose and he said the EGR valve was very dirty. He cleaned it and it tested good But, told me the EGR exhaust ports needed to be cleaned, per a tech service bulletin that identified the engine hesitation at the 1500-2500 rpm range in drive. I did the work myself which included drilling out the 6 EGR exhaust plugs and cleaning the ports. They were very carboned up. Good news is...that fixed the bad hesitation! It runs great! I paid $85 dollars for the diagnosis...keep it in your arsenal of repair info ! There were too many expensive parts possible to poke and hope at! Now, I have a general fault code for fuel system with the "check engine" lite. There is also an O2 sensor fault, but as described to me, it may indicate an imbalance in the exhaust and may be showing a problem farther upstream, not necessarily a faulty O2 sensor. My surging idle seems specific. I do know there is an "IAC" valve (idle air control) and right beside that on the engine is a "fast idle valve". (or solenoid?). Of course both are very expensive, but easy to change. What are your thoughts or comments ? Also, I'm concerned the O2 sensor may be bad and sending a signal to the computer to compensate for a "non" problem ! It's my understanding as well that the O2 sensor has to get to 600 degrees before it starts sensing emission balances. I think I may have to figure out how to test each component ? I'm clever, but not a mechanic by trade! Thanks again.
ANSWER: Eric, i have to start by saying thank you for providing me with alot of details. Lots of people lack that input which in turn requires me to do a lot of guess work.
Now start by replacing that O2 sensor ASAP. Not only do you have an associated CEL (check engine light), but, this is killing your fuel economy and about 10% of your overall power. I believe the EGR valve being carbonated heavily was the culprit for your O2 sensor failing.
Here is an informative link for your motor too
http://en.wikipedia.org/wiki/Honda_F_engine
What is the exact CEL code? The IACV is common for failing when the miles exceed 120K+. Take a multi-meter and measure the resistance between the 2 same color (black?) wires of the sensor. Should be between 10 and 40 ohms. If within this range then the O2 sensor is probably good but who knows with the EGR failing the way it was. Once these repairs are done the car needs to have the idle and timing set by a professional. Or if you have a digital timing gun you can do this too. The idle is set when the timing is 100%. Then you turn your headlights on and heater to full blast and adjust the idle to 850 rpms +/- 50 rpms. And/or i like to put the car in gear and hold the brake while i adjust. This bit of information should keep you busy for a while let me know in a follow up question if you have anymore questions or concerns.
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QUESTION: It was a while ago, but I believe the codes were 43 and 41. Thanks for your inputs! I agree that I (or someone) needs to test the O2 sensor! It is an $80 part! One comment though. I believe I read elsewhere that O2 sensors are often changed needlessly. It is my understanding they do not fail due to "carbon build-up". It's more complicated, but ties to silicone eroding the sensor composition. The sensor is their to specifically detect imbalance of exhaust gasses, to include carbon. It sends a signal to the computer which "adjusts" the engine based on those inputs. A failing EGR valve does not send a "code". It is the O2 sensor that suggests a problem in the EGR system . I really don't think timing has anything to due with the surging idle?? Timing is important obviously to be correct, but it was fine until EGR problems, and now a separate surging idle seems specific enough to diagnose directly. I would more tend to think if the timing were incorrect, it would affect more than just surging in idle in park?? I was hoping this problem was common and specific enough to help get a most likely cause. Thanks again for your ideas and inputs ! Another gee whiz fact is that the fast idle valve is regulated by engine coolant running through it and as it warms up, the valve moves to regulate air flow...I never thought coolant impacted idling!
AnswerUnfortunately these cars dont run forever and is sometimes necessary to purchase new parts in order to get the same or equivalent performance and reliability your Honda has provided. You have alot of time and precise - thorough - commentary. I hope if you have any more questions in the future you will come bact to allexperts.com
