Misfires while decelerating- not coasting

Dear Community,
My 1998 Honda CRV, automatic transmission, has 286,000 miles. The problem seems to be getting progressively worst, ie, the engine seems to misfire only when decelerating, most noticeably at highway speed -not evident during acceleration or while coasting. Also more noticeable when the engine is warm. I have used a bottle of injector / valve cleaner in the gas tank and I changed the fuel filter. My mechanic tells me that my front rotors are warped (but it seems if that were the problem, it would be noticeable during braking). The car needs a few other repairs but if I can’t solve this problem I do not wish to sink any more money into it. Appreciate any thoughts from the community…

The fuel supply is cut off during deceleration (DFCO). Misfire is not possible.
Whenever your foot is off the gas pedal and engine rpms are over 1200-1500.
All recent fuel injected engines use this gas saving feature.
My 1985 Accord SEi had it.

only when decelerating … not evident … while coasting”?
So, what’s the difference between the two?

At 286k miles you really need to run a compression test on this vehicle and especially so if valve lash has never been checked.

At that high a mileage there could be a misfire issue due to low compression. Given the mileage, one would hope for 150 PSI across the board. If you get readings of 100 PSI and/or the readings are not consistently close to each other on all cylinders that’s going to present a problem; a dying engine.

The IAC maybe dirty. Does it idle normally? Warped rotors cause a pulsing in the pedal and shimmy in the steering wheel. Can you give more of a description of what your symptoms are?

I don’t think it’s a misfire.
Here’s a WAG: bad inboard CV joint.

thank you for the input everyone:

circuitsmith: I know I’m using “misfire” liberally because I don’t really know what the problem is but to clarify, when my foot is completely off the pedal, there’s no prob. It’s when I’m easing up on the accelerator and still giving it gas when I notice the “apparent” misfire. As far as a bad inboard CV joint- by inboard, does that mean closer to the transmission? How would I diagnose that? …by attempting to move the drive shaft in two directions (at right angles) to the long axis of the car to determine if there is play in the joint?

ok4450: If there is a low compression issue, wouldn’t the symptom (feels like misfiring) be evident at instances other than deceleration as I clarified above?

knfenimore: Is there an easy way to clean / deal with a dirty IAC? The warped rotor possibility - I do not feel a shimmy in the wheel nor a pulsing on the pedal. As far as more description of the symptoms - beyond what I have described, it feels as though the vehicle is being tossed due to turbulence as if a large truck has pulled in front of me, or as if I were on a bumpy road. The apparent loss of power is very short in duration, ie I am able to maintain speed, but the jerks may be frequent, perhaps a slight hesitation every second. It will then go for a period of time (a couple miles) without any symptoms.

“when my foot is completely off the pedal, there’s no prob. It’s when I’m easing up on the accelerator and still giving it gas when I notice the “apparent” misfire.”

This key information changes everything.

I’d start by cleaning the MAF sensor if it has one and changing the spark plugs if they have a lot of miles.

Is this possibly another transmission problem? Lock up clutches chattering, lurching, bobbling, chuggling, whatever, are often the cause of what is first thought to be missfire.

+1 to a trans issue.
Drain and fill with Honda spec fluid is a good place to start.

Honda transmission service would be a good start. I would also have someone inspect your front end and cv joints

Thank you for all the thoughtful recommendations. All of the options presented here do not seem to be too involved so I’ll start on the list until hopefully I reach a solution and report back, probably not until early next week.

I would also have the motor mounts checked.

If you can tur off the OD overdrive and drive it. If it stops it will point at the tranny.

knfenimore: As a matter of fact, I believe one of the motor mounts is broken. I have been driving on it for >100K, I’m ashamed to admit. I don’t think there is an OD switch on the dash but I’ll take a closer look. I could put the shift lever in “4” as opposed to “D” if that would serve the purpose. Regarding your previous question, I “misspoke”- there is in fact a pulsation in the brake pedal as I apply the brakes, which points to the wrapped rotor condition I believe. I have much to chew on and will have a busy week end. Thank you for the information.

Didn’t some cars, probably some years past, have a “deceleration valve”? What was that for? Wasn’t it for changing the ignition timing during deceleration to avoid engine sputtering/backfire? I wonder if the OP’s problem could be related?

The first thing that came to my mind was valve timing, and perhaps burned valves causing combustion leakage into the exhaust manifold, but you may want to also consider leaking injectors. Under deceleration, vacuum is very high below the throttle plate, as the pistons try to draw air in past a closed passage. If you have injector leaks, the pistons could be drawing in enough fuel from the leaks to be feeding unburned fuel into the exhaust where it misfires.

I agree with OK4450 that a compression test is a good place to start. That’ll not only test for wear, but you should also find a burned valve if you have one.

A vacuum test is also a good idea. That’ll identify sticking valve issues, which could also be allowing combustion leakage into the exhaust manifold, as well as find vacuum leaks if you have them. Vacuum leaks can cause all sorts of erratic behavior depending on where they are.

The suggestions above are good ones. One thing to check early on: is the throttle plate sticking slightly open because of deposits in the throttle body?

I have cleaned this on my 1999 Honda Civic once or twice using a spray can of cleaner, and old T-shirt and a toothbrush. An old toothbrush.

I have checked valve clearances a few times and always a few needed adjustment.

I conducted a few of the more simple repairs without success. As it turned out the screw that retains the rotor to the shaft coming out of the distributor had completely backed out. The distributor shaft had bored out the rotor so the rotor was pretty floppy. After securing a new rotor the car started but died after one minute. After lots of trial, error and testing I changed the ignition coil. That did it. Just went for a test drive. Seems fine. 286,000 miles and still going. Thanks for all the input and support from the community.

Thanks for the update. When you change the ignition rotor it’s a good idea to change the cap too. They work together as a pair, and perform better if they wear together. Assuming you didn’t also change the cap, if you run into what might be ignition problems later, suggest to replace both the cap and rotor.

Good grief… That’s a new one on me. But the loose rotor possibly resulted in an extremely wide air gap which pushed the secondary voltage up and toasted the coil. Congratulations for having the persistance to find success @rogmut.