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2001 Honda Civic - Motor Sputters When Going Downhill

I have a 2001 Honda Civic LX with a 5 speed sedan that we bought brand new 19 years ago. The car currently has 179K on it. A problem that has stumped me is that when going downhill on the Interstate at speeds anywhere between 50 MPH - 65 MPH with no change to the amount of pressure being put on the accelerator, the car “sputters”. Specifically, the car acts as if it’s getting about 10% less fuel. (I watch as the RPMs usually “jump” back and forth around 100 or 150 RPM during the time the car is going downhill.) It’s pretty minor, and most people would not even notice. No check engine lights. The car just had about $2K of service done to it at the local Honda dealer (timing belt, new accessory belts, new spark plugs, valve adjustment, synthetic oil change, new radiator, new radiator hoses, brake fluid change, etc.) None of this had any impact on the problem, though. My thought is maybe dirty fuel injectors or a bad fuel pump, but these are just guesses. Any recommendations on where to start?

Have you had trans fluid changed?

Yes - manual transmission fluid was changed in March of this year.

I did not realize it was a manual transmission, sorry if I missed it. It sounds like you have done everything you can so far, hope someone has a good suggestion. Try some techron or seafome as a thought.

I’m thinking fuel pump. Maybe the pickup has been knocked askew or is leaking.

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Thanks, Barkydog, for your insight. The Techron or Seafome would both be low cost solutions, so I think I will give that a try!

I do think it’s a good chance it’s the fuel pump. I should say the car has had this problem for several years now, and it hasn’t gotten any worse or better. A few years ago, I asked the local Honda dealer to investigate it and they said the motor mounts were bad, so they replaced them. I just took a 1600 mile trip on the Interstate and the car performed flawless with an average MPG of 38.

Given how well it runs, no codes and the mpgs… Sounds like a quirk due to normal wear and tear and a sensitive owner/driver.

Couldn’t hurt to replace the pump. They don’t last forever.

Fuel pump would not be on my top 10 list for rpm surge when going downhill

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You say it is a manual transmission and you are witnessing rpm fluctuations. You do not say whether you are actually feeling these, or whether the speedometer is fluctuating. What is the rate of fluctuation?
Also, to be complete, I assume you are not talking about something happening when using cruise control.
How steep are these hills? Just steep0 enough that throttle is needed? Or so steep that you are off the throttle?
Is the word “Throttle” used anymore???

You might consider the possibility of scale or corrosion on the inside of the spark terminals inside the coil boots.

I suggest this because a long time ago I ran into a Ford 4 cylinder that would start right up hot or cold, idle as smooth as Rolex watch, and run like a top. Nail it to the floor from a dead stop or any rolling speed and not a hint of a miss.,
But, at certain points when the same pressure was maintained on the throttle the car would buck and jerk when the load was off the engine to some degree. The symptom was similar to running out of gas.

The problem was corrosion on the coil terminal. Cleaned it with a tiny wire brush and all was well after that. Hope that helps and for what it’s worth should have been checked when the plugs were changed although I don’t fault the shop on this matter. At 20 years of age it’s possible if those are the original coils.

I have a 1999 Civic EX 5 speed with similar mileage that I bought new. I would check for any play in the distributor shaft or corrosion or carbon tracking inside the cap; and clean the throttle body and edges of the throttle plate with the appropriate solvent, a toothbrush and a cotton rag.

Good luck! Please let us know.

Hi Oldnotdeadyet - I notice the RPM fluctuations, i.e., it goes from 2600 down to 2450 and then back to 2600, back to 2450, etc. And no, cruise control is not being used. Regarding the steepness of the hill, I would usually say about 45 degrees, but only when going down hill and not uphill. I have always just kept it in 5th gear when going downhill. If/when it was really steep, I guess I could downshift to 4th as necessary, but that’s rarely been the care.

ok4450 - I had not considered the corrosion on the inside of the spark terminals inside the coil boots - that’s one of the great attributes of this forum is that so many experienced individuals help everyone. What you describe sounds like an easy, inexpensive fix. And regarding the coils, yes, they are the original coils. I have all documentation from when we bought the car brand new from the Honda dealer 20 years ago and the coils have never been replaced.

I promise you that you have never gone down a 45 degree hill! When you see “steep hill ahead…check your brakes” signs, the hill might be 5 degrees.
I asked the question of whether you actually felt the RPM fluctuations as speed fluctuations. Or, are you just watching the tach?

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Good catch - you are right, I should have said 5 degrees. I both feel it and I watch the tach while it’s happening. It’s like the car is only getting 90% of the fuel amount it was getting a moment before, i.e., it’s sputtering (?). It’s somewhat hard to explain.

Here is a silly question: you believe that the engine is going back and forth between “not enough” and “just enough” gas. How do you know it isn’t going back and forth between “too much” and “just enough” gas? or even, “not enough” to “too much”?

Oldnotdeadyet - it is difficult to explain, but the impression I have is that some small amount of fuel (10%?) is not making it to where it needs to go. (Note: this car does not have a fuel filter, otherwise, I would have replaced it.) For these short periods of time (1 - 1.5 seconds), the RPMs drop approximately 100 - 150 RPMs (despite not change in the amount of pressure applied to the gas pedal), until the situation is resolved when I’m back on a level ground and/or I am going up a hill, where this then becomes a non-issue.

How do you know your symptom isn’t spark related?

Isn’t the fuel filter in the fuel tank ? What happens when you go downhill using the cruise control if it has one .

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