I recently inherited my grandfather’s 2008 Honda Civic (1.8L four-cylinder engine) that is good on gas, has enough pep for the yeoman work it performs and I won’t have to budget the cost to change a timing belt.
However, there is one nagging issue. Upon cold start, it idles around 900-1000 rpm and you could balance a cigarette on the dash. Once warmed up, the idle speed, according to the car’s tach, drops to a paltry 600-650 rpm. This results in a rough idle and noticeable vibration. The vibration can easily be felt through the headrest, or by resting my fingers on the dash or armrest. I don’t believe I have ever owned a four-stroke engine that idled this low, the norm seems to be in the 700-750 rpm range. The engine in question has only 20,000 kilometres on it, so wear is not the problem – it runs as smoothly as any engine I have operated, except at idle. Turning on the headlights or air conditioning bumps the idle up slightly and it smooths out somewhat. I don’t believe there is any mechanical tweak to adjust idle speed; it has to be done by reprogramming.
Given that a large percentage of these cars are driven in congested commuting conditions, did Honda do this deliberately, in order to squeeze more into the fleet fuel efficiency? There are millions of these 1.8L engines in use – is this rough idle issue a common complaint, and is there a fix for it?
I could just live with it, but it doesn't seem right. Modern engines – even engines from 40 years ago – idle smoother than this. I’m trying to find some background on the issue, so I can deal from an informed position with the dealer, as the vehicle is still under warranty.
Edward in Toronto
Edward, your observations of a wonky idle speed and adjustment are on the money.
Bad news first: Because of the low mass of rotating engine parts, new engines often exhibit idle vibrations. There simply is not enough mass to absorb power stroke pulses through the powertrain. This is exacerbated by the quest of vehicle manufacturers trying to comply with reduced exhaust emissions by lowering idle speeds as much as possible.
Now the good news: Idle speed can be adjusted on fuel-injected engines in a variety of ways, dependent on the manufacturer. In your case, there is an Engine Control Module software update. There are two versions of this update and it’s important that your dealer apply the latest version.
They may find reference to Service Bulletin No. 10-073, dated Nov. 24, 2010, but this is the old update. The new version uses the same TSB number of 10-073 – but supersedes this with a date of July 15, 2011. That’s the one you want.
The updated software must be Version: 2.020.018 or later. After installation, you should notice a rise in your idle speed to 750 rpm (plus or minus 50 rpm). This is the Canadian spec and is used for manual and automatic transmission-equipped Civics. If your car has the automatic box, the idle rpm is measured in Park or Neutral.
Even more good news: this adjustment should be covered under the warranty provisions.
Given emission control specifications, I hope this is the end of your vibration – tipping over a cigarette can make a real mess of the interior.