Vibrating/Rough Idle in Honda City 2001 EXIS

[k180233]

Hi guys, I hope you guys are doing good.

I have an Honda City 2001 EXIS Automatic, and the issue I am facing is that the car vibrates on low RPMs, specially at idle.

About roughly 2000 Kms back, I got my spark plugs, fuel injectors replaced. Also got its Throttle Body cleaned. The engine runs very smooth as soon as I am not at idle, there is no misfiring in engine or anything, no check engine light or anything.

I also got my car scanned, got no error codes, manually monitored sensors performance everything seems to be running fine. Below I am providing a basic summary of what were the ECU reporting when at the time of manual monitoring.

Car starts, no load RPM @ 1000, IAC valve @ 20-22%
I put the car into gear D/R from P, RPM @ 750, IAC valve @ 28-30%
Switched the AC on, RPM @ 625-650, IAC valve @ 40-42%

The above clearly shows ECU is responding to increasing load and opening IAC valve to compensate the increasing load, but still the RPM drops.

The car has never stalled at idle, and other than just annoying vibrations at idle, haven't faced any problem. Apparently my mechanic doesn't wanna loot me, so he says that your car is running fine and you are just thinking too much, there isn't any problem and you clearly don't need another throttle body cleaning just after 2000 Kms.

But personally the vibrations annoy me, and I want to get rid of them. Can anybody please tell me if he has ever solved this issue?

PS: It has a Honda D16 engine.

[Proverbial_Slang]

Does this happen at cold engine or warm?

[k180233]

Happens at both. No matter whether I have just started the car or have driven for a few minutes. As soon as I am at idle and the car isn't in Neutral/Parking, RPM drops and engine vibrates.

[Proverbial_Slang]

I thin it is the IAC valve then. It could also be a leaking vacuum pipe. Check the PCV valve as well.

[k180233]

My first guess was IAC valve too, but it was cleaned just 2000kms back along the entire throttle body.

I also mentioned vaccum leaks to mechanic and he said in case of a vaccum leak you'd be having higher RPMs at idle rather than lower.

Will get PCV checked along with spark plugs, I feel like one of them might be the culprit too.

[supraman2jz]

In idle position, remove the IACV grip and see if it has any affect on idling, this would rule out a working/not working IACV. I would also think it's the IACV.

[Proverbial_Slang]

That's a good idea. I had a dirty and partially stuck IAC valve and that is how I checked it.

[supraman2jz]

Yeah, if you have an older Honda, that is how you check for working sensors on the go lol

[k180233]

I got IAC valve checked yesterday, it's working fine.

I now started to feel at times sluggish/hesitant acceleration under load i.e. 3/4 people in car with AC on, also at times I felt car jerked like a very minor misfire once in a 20-25 mins drive, so I started suspecting spark plugs.

Asked mechanic to check them out and the gap between electrodes was significant, so apparently that's what causing poor performance and idling problems. He managed the gap for now, asked me to not change plugs right away unless misfiring becomes a bit common/prominent so he can diagnose exactly if it's plugs or anything else wrong with ignition like coil etc, as right now misfiring hardly happens, maybe one or two very minor misfires in a 15-20km drive.

Should I change the plugs right away or should I wait for the problem to become prominent to be diagnosed correctly?

Anyway, thanks for your help guys!

[Proverbial_Slang]

Plugs are a cheap replacement part, s change them to get it out of the way.

[supraman2jz]

How is your ignition timing? Have you gotten that checked yet? If not, get it checked via a timing gun.