I have a 2002 CR-V with and M/T that has been experiencing erratic idle issues since bought used. Simply, revs hang with clutch in at about 2,500 rpm on 2-3 shifts around 20 mph when cold. I am chasing the theory that this is the window when the purge control valve opens and there is a vacuum leak in the system. I have replace the solenoid actuated valve on the TB and replaced the downstream test valve with a straight piece of vacuum line to try to isolate the problem. That gets me to the firewall. No luck. In an effort to test the rest of the system all the way to the canister I am wondering if I can go low positive-pressure via compressor at the firewall and listen for leaks. Just wondering if this will damage anything and how much pressure to use. Thanks for any help.
Danger in pressurizing EVAP purge
- Thread starter jtfmdyk
- Start date
- Status
I think your theory is defective, fuel system is sealed unless canister vent valve is stuck open. If you have a maf sensor a leak after the sensor will cause a lean condition, without the addition of fuel and air it wont idle fast. If you really want to check it just plug the intake where the hose attaches. That will eliminate the whole purge syste.
I think you are barking up the wrong tree. Just an opinion.
If a purge valve hangs it will usually code, and sometimes cause a rich stumble, and in some cases the engine will die on decel. If there is an actual evap leak, your PCM should catch it during the EVAP tests during normal driving. EVAP tests are really picky and even a tiny leak, one that would not be big enough to cause a driveability concern, would code.
Any codes? Any service bulletins for the concern?
If it is fly by wire, you could have a throttle body fault, if it is not fly by wire, suspect a TP sensor not returning to base voltage when you let of the accelerator. The dashpot function is either controlled by the throttle body, or the IAC. In the case of an IAC if the TP sensor doesn't show closed throttle, it defaults to wide open and causes engine revving, and it usually doesn't set a code.
You can pressurize the system, but using only really low pressure, a fraction of a PSI, but usually any component open to atmosphere on the purge valve side of the system will be caught during continuous tests.
Good luck with this.
If a purge valve hangs it will usually code, and sometimes cause a rich stumble, and in some cases the engine will die on decel. If there is an actual evap leak, your PCM should catch it during the EVAP tests during normal driving. EVAP tests are really picky and even a tiny leak, one that would not be big enough to cause a driveability concern, would code.
Any codes? Any service bulletins for the concern?
If it is fly by wire, you could have a throttle body fault, if it is not fly by wire, suspect a TP sensor not returning to base voltage when you let of the accelerator. The dashpot function is either controlled by the throttle body, or the IAC. In the case of an IAC if the TP sensor doesn't show closed throttle, it defaults to wide open and causes engine revving, and it usually doesn't set a code.
You can pressurize the system, but using only really low pressure, a fraction of a PSI, but usually any component open to atmosphere on the purge valve side of the system will be caught during continuous tests.
Good luck with this.
Last edited:
What diameter is the line involved? Usually it's around 1/8 inch which is too narrow to raise your idle that much. How about removing the solenoid, if able, and having its port temporarily open to atmosphere, eg a temporary permanent vacuum leak?
Typically the idle air bypass opens as a "dashpot" on stick shift cars for emissions reasons, to blow hydrocarbons through when the system is surprised by sudden clutching or releasing the gas. This leads many newer cars to idle high when rolling and shifting.
This could throw a code, but if you unplug your idle speed controller motor with it positioned at "regular idle" I bet your mid shift revving will control itself.
Typically the idle air bypass opens as a "dashpot" on stick shift cars for emissions reasons, to blow hydrocarbons through when the system is surprised by sudden clutching or releasing the gas. This leads many newer cars to idle high when rolling and shifting.
This could throw a code, but if you unplug your idle speed controller motor with it positioned at "regular idle" I bet your mid shift revving will control itself.
I am not one to run to the mechanic for a fix, but I have learned thru the years that cars are now to complicated for us older shade tree dudes. If its got codes and egrs and evaps, I would suggest you find someone that does that all the time to fix it imho
Thought: call a specialist, ask those guys at Napa, az, for a reference, they usually know a geek that can fix it.
Thought: call a specialist, ask those guys at Napa, az, for a reference, they usually know a geek that can fix it.
Evap. system is usually checked with a smoke machine. Idle Air Control Valve is something worth looking into. In addition I usually find the valves need adjusting on Honda's (too tight, will not make noise like loose valve adjustment). So it only does this in open-loop operation? How long does it hang if you leave the clutch pedal depressed? I imagine you are not talking about the feature that keeps the RPM's up briefly between gear changes?
If you really want to check it just plug the intake where the hose attaches. That will eliminate the whole purge syste.
This^.
It may not like having no venting in the gas tank. It may throw a code. But you should see real quick if that half is good/bad.
This^.
It may not like having no venting in the gas tank. It may throw a code. But you should see real quick if that half is good/bad.
Last edited:
Thanks for all the feedback, I will start chasing down some of these suggestions.
- Status
Similar threads
