My car RPM drops significantly when braking with clutch pressed

[nauman.hanif.9]

i have 98 civic with dual vtec D15B, the rpm remains stable and gives no problem when the car is idling.
while cruising, as i apply brake with clutch paddle pressed, the rpm drops signifcntly in petrol and the problem is more sever in cng. the rpm drops to zero and i have to start my car again or shift down to a lower gear and then release the clutch and the engine would start again.
i cant use the CNG anywhere in local, just on motorway and that too as far as i dont use the brake.
the assembly is new, spark plugs are new, throttle body is cleaned, air filter is new. tuned my car a hundred times in cng but it doesnt solve the problem at all...................

[ZainMahdi]

If the rpm drops very suddenly before the engine stops, it could be a worn out dashpot. The dashpot slows down the throttle closing when the driver lets off the pedal, so the rpm drop is slightly slower. This prevents a sudden rich condition for the engine, starving it of air and causing it to shut off.
The dashpot is supposed to be connected to the throttle body.

[nauman.hanif.9]

where is this Dashpot and what is the name commonly used for this thing?

[nauman.hanif.9]

what is dashpot?

[argtr65]

First of all isolate the problem,either it could be because of voltage drop or heavy vacuum leak.
To check voltage drop disconnect the brake light by removing wires from brake light switch or fuse from fuse box,then apply brake and see the result,if there is no rpm drop,then check brake light wiring for bad connection and short circuit and as well as alternator's out put voltage at idle rpm.
If problem remain persist then check the brake booster and its fittings.

[nauman.hanif.9]

the brake voltage drop has been checked, even if i have not applied brakes and just press the clutch pedal whille cruising, my RPM drops to zero........ it drops to 200-300 in petrol, and in CNG it drops to Zero

[adeel86]

Have ur tappet adjusted when engine has been shut for more than 6 hrs vtec engines required to be dead cold for adjustment I had a similar problem and my tappets were tight remember it's very important that engine is cold like less than 38c hope that helpps

[pwuser149081906924]

I had the same problem, and i live in karachi, if u live in karachi, then go to cng kit zone, jail chowrangi,change ur emulator plus advancer 2 in one kit rs 3500 along with new wiring and fitting cost. Then run your car on cng , i had observe that after a week a tik tik sound coming from cng switch and then the cng conversion switch failed, then i go back to cng kit zone and change my switch, and add a the additional wire for earth, then i drove 50 km on cng, and the main problem was resolved pressing clutch on cng with ac resolved, switch cost with earth wire costed 700.

[pwuser149081906924]

Its basically cng advancer plus emulator plus bad cng conversion switch and earth problem, i m enjoying now the ride now on my idsi 2005.

[sohelahmed]

wiring issue...or check after cleaning throttle...

[aliasim.asim]

My 2010"honda city has the same problem andI am totally baffles with it. Whenver I have to change the gear the rpm drops very quickly and after the gear change the engine take a little jerk to get back to the high rpm. The problem becomes worst when the ac is turned on, rpm drop is very significant and can go from 3000 to 500 as soon as clutch is engaged. My mechanic says fuel filter has to be changed but I dont agree with him, I think there must be something that reduces the rpm drop when driver lets off the gas and that thing is not working propoerly. My guess is the same like zainmahdi, the dashpot must be bad

[roony]

clean the throttle body, that helps.

[uzair3337]

Did you found the reason?

[letnikov46]

Hi, any update on this issue? I have this same situation on my civic 1.8 2008 sedan version. Petrol or cng doesnt matter, brake or no brake, when i press clutch the rpm drops to 400/500. But most is noticeable when i go downhill, while using the motor braking and applying a tad bit of brake pedal and in the same time shifting to neutral. This happens mostly in lower gears, whenever I disengage the clutch