repiv
07-10-2008, 10:17 PM
We've seen it time and time again over the years and recently, we've seen a lot of posts about how when an S2000 comes to an intersection and the clutch is pushed in, the idle dips waaay down and the engine starts to shake like crazy, nearly dies and then comes back, only to do it again at the next stop. This seems to be a very common characteristic of the S2000 going way back to when it was brand new. I have expounded upon my theories as to why this happens on many occasions. I won't go into again, at least not immediately. Suffice it to say that this car's "high race" nature of the cam profiles has something to do with it and how the ECU tries to manage the situation using various sensor readings.
I've noticed over the years that whenever climatic conditions change dramatically from day to day and from season to season, this low idle, near death condition becomes prevalent and we see increased reports of this on various S2000 forums. I even get more PMs about it when it happens. Most people just attribute it to "heat bog" and some even demand that Honda fix this "fault". Heat bog is one cause and is an easy out or excuse for why this happens. However, I have also noted that even on only warm days, before the intake air gets hot, this can happen. I've noticed this lately as our humidity has climbed and as it fluctuates wildly between under 30% to over 90%. Well, many people live in high humidity conditions and don't report this phenomenon at all. I would now further suggest that it isn't just high humidity that is a factor but rather, the change to high humidity that can do it. Both of these things can contribute to the engine having less power output. Every engine requires a certain amount of power just to run itself against its own friction and resistance. By shifting the power curse down due to heat and humidity, the power available near the normal idle rpm may no longer be enough to keep the engine spinning. It hesitates and takes a momentary dip till the ECU can sense this and "catch it".
It has also been noted that the use of the air conditioner can also aggravate this condition due to the additional parasitic load on the engine at low rpm. Recommendations range from getting a cold air intake to reduce the heat bog problem to cleaning the Idle Air Control mechanism to doing the "MAP whack". All are good suggestions and in many cases, will resolve the issue (for a little while).
People with this problem indicate that they repeatedly give it gas to keep the idle from falling so low, only to discover that it doesn't help at all and the condition persists. When questioned about their driving technique, more often than not, the driver admits to pushing the clutch in very early (far from the stop while still moving at a good road speed). They tend to "coast" a good distance before coming to a stop.
My recommendations have always been to give the ECU a chance to learn to deal with this. There is a caveat to this advice and that is that maintenance of the car must be up to snuff. You can't have a filthy air filter or really fouled sparkplugs or clogged injectors. These things complicate matters considerably and need to be addressed first. A car that actually "dies" when the idle dips low is a sign that something else is wrong and these things must be dealt with accordingly.
So, how do we combat this annoying dipping idle thing? My recommendation has always been to NOT "help" it by giving it gas when the rpm drops low. Don't touch the gas pedal at all. Let it dip. That's the best way for the ECU to see what's going on. Altering the throttle position only throws in another variable that the ECU must contend with.
Next, DON'T push in the clutch prematurely when coming to a stop. Get into a driving habit of downshifting through the gears as you slow down. In most situations, we don't go into first till we've come to a stop or a near stop. Therefore, as we approach the stop, leave the clutch alone till the rpm gets to about 1000 rpm or even just below. THEN push in the clutch in preparation to come to a stop or in preparation to put it into 1st to get ready to move off. You will be surprised at how many people have tried this and have resolved this dipping idle thing. There's really nothing wrong with the car. It's just that under certain conditions, the ECU has a lot to deal with and using this technique is the best way to help the ECU sort it all out for itself.
So next time you get the "near death" experience, give this driving technique a try and see what happens.
I've noticed over the years that whenever climatic conditions change dramatically from day to day and from season to season, this low idle, near death condition becomes prevalent and we see increased reports of this on various S2000 forums. I even get more PMs about it when it happens. Most people just attribute it to "heat bog" and some even demand that Honda fix this "fault". Heat bog is one cause and is an easy out or excuse for why this happens. However, I have also noted that even on only warm days, before the intake air gets hot, this can happen. I've noticed this lately as our humidity has climbed and as it fluctuates wildly between under 30% to over 90%. Well, many people live in high humidity conditions and don't report this phenomenon at all. I would now further suggest that it isn't just high humidity that is a factor but rather, the change to high humidity that can do it. Both of these things can contribute to the engine having less power output. Every engine requires a certain amount of power just to run itself against its own friction and resistance. By shifting the power curse down due to heat and humidity, the power available near the normal idle rpm may no longer be enough to keep the engine spinning. It hesitates and takes a momentary dip till the ECU can sense this and "catch it".
It has also been noted that the use of the air conditioner can also aggravate this condition due to the additional parasitic load on the engine at low rpm. Recommendations range from getting a cold air intake to reduce the heat bog problem to cleaning the Idle Air Control mechanism to doing the "MAP whack". All are good suggestions and in many cases, will resolve the issue (for a little while).
People with this problem indicate that they repeatedly give it gas to keep the idle from falling so low, only to discover that it doesn't help at all and the condition persists. When questioned about their driving technique, more often than not, the driver admits to pushing the clutch in very early (far from the stop while still moving at a good road speed). They tend to "coast" a good distance before coming to a stop.
My recommendations have always been to give the ECU a chance to learn to deal with this. There is a caveat to this advice and that is that maintenance of the car must be up to snuff. You can't have a filthy air filter or really fouled sparkplugs or clogged injectors. These things complicate matters considerably and need to be addressed first. A car that actually "dies" when the idle dips low is a sign that something else is wrong and these things must be dealt with accordingly.
So, how do we combat this annoying dipping idle thing? My recommendation has always been to NOT "help" it by giving it gas when the rpm drops low. Don't touch the gas pedal at all. Let it dip. That's the best way for the ECU to see what's going on. Altering the throttle position only throws in another variable that the ECU must contend with.
Next, DON'T push in the clutch prematurely when coming to a stop. Get into a driving habit of downshifting through the gears as you slow down. In most situations, we don't go into first till we've come to a stop or a near stop. Therefore, as we approach the stop, leave the clutch alone till the rpm gets to about 1000 rpm or even just below. THEN push in the clutch in preparation to come to a stop or in preparation to put it into 1st to get ready to move off. You will be surprised at how many people have tried this and have resolved this dipping idle thing. There's really nothing wrong with the car. It's just that under certain conditions, the ECU has a lot to deal with and using this technique is the best way to help the ECU sort it all out for itself.
So next time you get the "near death" experience, give this driving technique a try and see what happens.