89 Accord-Intermitent rough idle-hot weather

[mharris251]

I have a 1989 Accord LXi , automatic w/ air. I am experiencing sudden and intermittent rough idle and rough acceleration. This only happens in the spring and summer on warm or hot days after the car has been parked outside. IE in a parking lot.

Initially the car starts and runs fine and then within a few blocks in begins to shake and idle rough at the first or second stop. I must pull over and restart the car. This may happed several times. After that the car runs fine

Occasionally the check engine light will come on and a reliable mechanic advises me the code indicates “throttle body sensor”. However the sensor tests ok. This mechanic advised it may even be a bad wire somewhere related the throttle body sensor

I recently had a problem with fueling the car that could be related. I could barley get it to take the fuel without constant splash back. I noticed a lot of vapor pressure upon removal of the gas cap. The cap is not vented and it’s the correct cap. I’m wondering if this is part of the problem like some sort of vapor release mechanism is not working under the hood. Our recent smog check indicates the catalytic converter is down to its last few years ( it did pass smog/California car)

What could be wrong? Only happens in the summer, especially when its really hot. Never happens in the winter.

Thanks
Mharris251

[jeffcoslacker]

I think you are right, there is a connection...I'm thinking fuel tank pressure solenoid or tank vent is malfunctioning and the tank is overpressurizing,

It would be an interesting experiment to see if when it does it, get out and remove the gas cap before attempting a restart and see if that relieves the problem...if it seems to consistently, I think you nailed it.

It could be actually pushing fuel up the vapor system, when the engine starts the purge solenoid opens to burn the fuel vapors collected when the tank gets hot from sitting...if it's pushing fuel into the vapor recovery system it will run very rich and poorly until the excess fuel is burned off or the pressure is relieved....

Unfortunately I can't tell you exactly how the vapor system is set up in your car, GM is my specialty...but they all work on pretty much the same principles..the tank will be vented by a mechanism, either mechanical or electrical, that allows air in from the atmosphere to replace the fuel being pumped out, and then that mechanism closes when the motor is not running, and pressure that builds is shunted to vapor canister for holding until the motor is restarted...then the purge mechanism opens the canister to the intake via a large vacuum hose, and the vapors are drawn into the motor and burned...this also helps enrichen the mixture at start-up, which the motor likes...