mysterious rough idle issue

[Xavier]

For a while now I have had a shaky idle and I’m getting out of ideas to fix it.
I did read the “how to solve honda idle problem” but couldn’t fix mine.

The car is a 2001 Honda Accord 4cyl 5spd.

No CEL
no stalling
MPG is good
power is good
spark plugs are good
IACV clean
EGR passage clean
coolant bled
valve lash adjusted (might have to redo)
front and rear mounts new
vacuum gauge showed 22inHG

engine idles at 750 rpm
shakes up to 1k rpm then smoothes out.
A/C at idle makes it much worse
rear defrost, headlamps also makes it vibrate more

I’ll provide any additional info
any help is appreciated
ty

Topic

[Kevin]

Good tests so far – have you checked for codes or history despite the lack of CEL? This may be able to do it quickly (well, it is quick if there are no codes):

What does a power balance test show? If I recall from my friend’s Honda engine of that era this should be quite simple to do. http://www.ericthecarguy.com/faq/solving-automotive-performance-issues?start=3

Just be careful during the power balance test – if for some reason the car loses power, be mindful to turn off the AC quickly. I have heard dreadful rumors that running the AC with the engine off for extended periods can damage it so I am very mindful of even a short duration.

Is it possible to test the fuel pressure? This may not help but if it is on your bucket list it would not hurt (I am never looking back, myself):

1. Is it within spec?
2. If you give it some gas, does the pressure raise momentarily then lower, or lower and struggle?
3. If the fuel pressure regulator runs off of vacuum, does disconnecting that have any difference?
4. Any other test your maintenance manual recommends.

From what I know fuel pressure regulators which run off of vacuum can also be tested by disconnecting their vacuum line and seeing if they leak liquid out of the vacuum port within 1-3 minutes. No guarantee that a lack of fluid means it is good, but it could prove it is bad.

Is the fuel filter due to be replaced? If so, if you disconnect the outlet side (be careful of spilling gas – I think the filter is in the engine compartment!), THEN disconnect the inlet side, does the inlet side have pressure as if it were clogged? Is it cheap and easy to replace and need to be done every so often anyways?

If you give it some gas when it does this, does the idle even out or stay rough even with additional RPMs? If you shift into drive when it happens does that suddenly cure it or change it at all?

I am not sure that any of the above will help but they should not hurt to add to your list of tests and they are what I would do to start (in addition to a many you have already done, of course).

[Xavier]

No CEL confirmed.

I am confident that my engine is in good condition. I remember doing a compression test, leakdown? test and fuel pressure test. I didn’t go any further because I got good results. That was about 10-15k km ago. The engine now has about 157k km, it’s still fairly… “young”

I did the power balance test. Any spark plug wire I disconnected made the engine angry.

I disconnected the FPR vacuum line, while preventing change due to vacuum leak. Doing that didn’t seem to affect the idle in any way.

There is no fuel filter on this car. Only a screen in the fuel tank.

The car is a manual. Only the idle is rough, between 750 and 1000 rpm. I have not noticed any other issue. If I slowly raise the rpm, it’ll keep the shaking low until 1k rpm. If I press harder on the accelerator, the engine vibrates quite a bit then smoothes out after 1000 rpm

I also used TKO 2000 fuel system cleaner through the intake manifold and seafoam through the intake tube. It seemed to have made the idle just a bit smoother. I also filled the tank with premium gas. I did these after talking with 2 mechanics/techs.

I’m thinking that since the only previous owner ran the car like a 200 years old woman, maybe there is some pipe/line somewhere that’s filled with gunk or carbon deposit.

[Bill]

First thing to do is a compression test. If the compression is reasonably equal between cylinders I would be having a second look at the engine mounts.

[Xavier]

this is definitely not a compresion issue. I remember doing a comrpession test in school. all cylinders were in very good shape and well within specifications. front and rear mounts are brand new. I installed them myself.

I also had the injectors cleaned and tried a distributor from another accord. none fo these fixed the issue.

I have had no luck finding a scan tool with live data so far.

Edit: I ordered a blutooth obd2 thing from ebay.

Edit 2: balancer shaft was out of sync

[Author]

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