Rough idle after VTEC - B18C7

[richie]

Hi Guys,

Car: dc2r B18c7

So I have been having this issue for a little while now and I cant seem to find out whats wrong.
Everytime I bring my car to vtec and come to a stop, the car idles rough like its on 3 cylinders.
Then everytime I bring the car to vtec again after the rough idle comes, it idles nice and smooth.
To maintain a smooth idle I just resist from going to high rpms and the car idles fine everytime. Its just when I feel like giving it a bit the idle runs really rough afterwards..

Another odd thing I have noticed is that if I blip the throttle from idle and let the idle drop again, the idle droops for a bit down to 600-500 like its about to stall then slowly climbs back up.
The car seems to respond slowly to electrical components being switched on i.e. A/C. Slowly as in the idle will go rough when A/C is switched on then climb to the 1000 mark after 15 seconds.

Anyone here come across this issue at all? what to look for next?

Things I have done so far:
-distributor cap and rotor
-spark plugs (changed about 40,000kms ago) and leads
-cleaned IACV
-cleaned throttle body
-replaced coolant temp sensor
-cleaned injectors


Thanks in advanced

[tinkerbell]

did you reset the ECU?

what do the tips of the spark plugs look like?

how did you clean the injectors?

have you checked for a vacuum leak?

[richie]

ECU has been reset for most of these jobs.

Haven't checked the spark plugs, they are ngk iridium ix plugs btw. Just worried I would get the clearance wrong if I were to reinstall them.

I took it to a mechanical spare shop to get them cleaned and checked. replaced all o-rings while I was at it.

I did vacuum leak test by covering the tb with my hand and did another test with carburetor cleaner squirting around the vacuum lines. (although im not sure if I have checked all of them since I dont know all of them)

[richie]

I also changed the coilpack when I changed the distributor and rotor.
Although its not original.. just some random brand I picked up from the mechanical spare shop. Could this be a cause?

I plan to change the vtec solenoid gaskets because I suspect that the plunger may be stuck? I also noticed that b18c7 don't have a oil pressure sensor on the solenoid, so cant really test that.

[tinkerbell]

dodgy coil can cause this issue,

but since your description of the issue is so vague (i know it is very hard to put such descriptions in words!!!), it is hard to know...

can you do a video of the problem?

i do not understand "I bring my car to vtec and come to a stop, the car idles rough like its on 3 cylinders"

do you bring it to VTEC while stationary in neutral?

or you are driving to VTEC then stop the car?

[richie]

Sorry i tried not to word it like "when I hit vtec yo!"

Basically while driving and engaging vtec and then coming to stop, at the lights for example.
At this point the car would start to idle rough.

Its hard to video since its more of the 'feeling' when the car is idling.
When the car is idling normally, I don't feel much vibration.
When the car is not idling normally (rough), It feels like the engine is lumpy, but the idle is only 50 rpms less than normal.

I can video the idle dropping though.

[richie]

Update on the situation so far:
spark plugs have been double checked and they have the usual carbon but nothing dramatic.

Could my fuel pressure be a problem? is it common for the fuel pump to fail intermittently? or Fuel pressure regulator? Relay?

[tinkerbell]

give the throttle body adjustment screw a a couple of turns counter-clockwise and see if that changes anything?

[tinkerbell]

if you can got into VTEC with out blowing the engine up - your FP should be OK...

[hello]

how did you clean the iacv?

[Karl]

exhaust leak. be my guess

[richie]

There is not idle adjustment screw for B18C7 im pretty sure.. I have a spoon venturi throttle body and it doesn't have one either.
Cleaned the IACV using throttle body and carby cleaner.

Anyway I have found my problem!

I have low compression on cylinder 3. Which means its either the intake or exhaust valves or piston rings...
I have a good feeling that it is the exhaust valve, because putting a piece of paper behind the exhaust tip flutters the paper in towards the pipe then out away from the pipe.
Getting it fixed soon.

Thanks for the input guys.