I don't know if this is an issue with you guys but it seems that sometimes when I clutch in my revs drop a bit and it sounds like the engine bogs. So here's my scenario:

I'm driving ~45mph and I see a stop light up ahead. I keep the car in 4th and brake without clutching in. When the revs get to 1.5k I clutch in and let the car cruise to a stop. Now sometimes when I do this the revs drop below 1k and it seems like the engine bogs.

I've tried clutching in at ~1k or a little below while braking in 4th and the car doesn't seem to bog when I do this. The only explanation I can think of is that clutching in too early drops the revs too much. Either that or something is wrong with my MAP sensor or maybe I need a new air filter or something. Is this a normal thing or is something wrong with my car?

 

I don't think I've ever let it engine brake down to 1.5k rpms in 4th gear.

I'll either go to neutral earlier or rev-match down gears (when decelerating to a stop).

People sometimes say to always be in a gear in case you have to accelerate out. But in 4th gear at 1.5k rpms, you're going to have to downshift if you want to accelerate anyway.

So if there's a chance of needing to accelerate, I'll downshift through the gears. If there's really nothing around, neutral.

 

my car does this as well. haven't figured out what it is.

 

^to CKit, this is only if you plan on stopping. i'm sure the OP doesn't let it drop to 1500rpm if he plans on accelerating any time soon.

 

mine is the same... if you push in the clutch kinda quick then it seems to just drop a fair bit 800rpm sometimes 600rpm then rises again... kinda odd. Thought it was a MAP prob but haven't tried locating the prob and fixing it yet...

 

I know, but if that's the case... why wait so long to clutch in and get out of gear?

 

Seems to be totally normal behavior. IIRC, XViper wrote a thoughtful essay about idle rev-dips, um, elsewhere. Bottom line is to let it happen and don't try correcting by adding throttle.

 

not sure if this is the same thing...probably not, and i've noticed this in my S2000 and Prelude...

If I engine brake in 2nd gear and i'm at 1k rpms or so the car slightly kicks foward and then cruises at idle. I'm pretty sure it's normal, just curious what's happening there.

 

When you are coasting in gear above a certain RPM threshold (usually somewhere between 1K and 1.5K), the engine shuts off fuel flow completely, meaning the car is using zero gas. Nearly all modern fuel-injected cars do this, even a lot of cars with automatic transmissions. This is why it is smart to leave the car in gear for as long as possible, because you maximize fuel economy by doing so. It's the difference between infinite MPG while coasting and (very roughly) 40 MPG @ 20 MPH while coasting. Infinity > 40. It adds up, especially if you're stopping a lot.

Now is where I start completely guessing: There may be a slight delay engineered into the switch between full cut-off and regular idle fuel flow. I could see them doing this to reduce jerkiness and lurching when driving very slowly in first gear. It would give you a second to put the clutch in after letting off the throttle without having the car lurch forward on idle throttle into the car in front of you. So if you're pushing in the clutch quickly at 1.5K RPM, then the revs may drop just fast enough to fall slightly below "idle" before the computer re-engages fuel flow. My guess is Honda felt whatever the delay is was a happy medium, and I wouldn't worry about it or try to change it.

Incidentally, I bet it doesn't do this when dead-cold. Most engines I've driven don't allow fuel-cutoff until the engine has warmed up.

A ScanGauge II is a great and easy tool to monitor fuel cut-off, MPG, and lots of other cool information in any car with an OBD-II port.

 

This is the car switching from fuel-cutoff (full engine braking) to idle fuel flow, which in 2nd gear is apparently enough to let the car creep forward without stalling.