Hi, i have a 1990 Honda Accord LX 4-door...Ive been having a problem with the idle going up and down (between 1000 and 2500RPM) when idling in park...if i put it in drive...it idles properly.

Well last week, the car started to kill on me...i would drive, get up to about 30-40mph and when i breakdown to come to a stop, the idle would get really rough and once stopped, it usually shuts off. If i let it warm up for a long time (at least 20 min) it will still get really rough, but wont shut down nearly as often.

I have replaced the entire distributor assembly (new dist., cap, rotor, icm, internal coil. new plugs and wires)...i have replaced the IACV...i adjusted timing and idle, i took off the "cold" part of the IACV and cleaned that out...I have used some air intake cleaner int he throttle body...i also took down the main relay and resoldered it.

The problem is still there, i have no idea what to do..the car always starts right up and idles forever...it will accelerate like it always has and runs perfect, the only problem is when im coming into a stop after accelerating or maintaining speed...Im thinking there is sufficient fuel and spark...im thinking its an air or air/fuel problem...any help?

P.S. there is no check engine light...Thanx.

 

My '92 honda accord had the same issue where, only when in idle, it was rough and sometimes would shut off too. My battery connections were getting pretty bad (it had some wet liquid on the battery terminals), which semi-blocked the electrical current flow. I disconnected the battery terminals, dried and cleaned them. I've been fine since.

I've had this happened to me a few years ago too on the same car when the battery terminals started forming corrosive materials. After cleaning it I was fine again.

One strange thing is that if I disconnect my battery and reconnect it, the car will idle rough for maybe 1-2 days before it becomes normal again.

 

High Idle speed and Fluctuation troubleshooting

Leaking EACV- Disconnect EACV connector. Idle speed should decrease. With the connector disconnected block the hole in the intake port or pinch the hose from the air cleaner to the EACV. If the idle speed decreases the valve is leaking. This condition will not set a code. The ECM can only detect an open or short circuit. It also may clog it’s screen if it has one.

Leaking IAC- (Idle air control valve) Disconnect IAC connector. Idle speed should decrease. With the connector disconnected, block the hole or pinch the hose to the IAC valve. If the idle speed decreases the valve is leaking. May not set a code and may not be a codeable circuit on all models.

TW or ECT sensor- (engine coolant temperature sensor) voltage should be about 3.0 volts @ 60 deg F and between .55 & .7 volts @ normal operating temp. If the voltage is above .8 volts at normal operating temp, will cause rich mixture and high idle speed. May not set a code because it is not far enough out of its operating parameters. **Also this sensor will not read temperature correctly if coolant is low. (beware)

Vacuum leaks- a loose vacuum hose or leaking intake manifold gasket can cause high idle speed and/or fluctuation. Also check for bad PCV valve.

Fast Idle Valve- (if equipped) a fast idle valve that is sticking can cause high idle speed and fluctuation. Check it by removing the steel cap on the top and putting your finger over the hole in the middle of the seat under the cap or block the port just inside of the throttle body opening, when the Idle is fluctuating or staying high. When the engine is warm this valve should be closed. You can tighten the seat but it will also change the idle speed warm up values (closing).

Throttle valve- throttle position sensor voltage should be .5 volts with the throttle closed. Make sure the throttle valve is fully closed and voltage is within spec.

ECU-If all else is good, if you reset the ECU and the problem goes away temporarily, the ECU may be defective.

Verify that the cooling system is full of coolant and
there is no air in it.

Remove the air boot from the throttle body and cover the
throttle body with something that will stop the airflow
(your hand, tape) with the engine running. With the
throttle body covered and no air going into the engine, the
engine should stall. If the engine does not stall, look for
a vacuum leak. With the engine running and the coolant
temperature above 90 degrees F, verify that there is no
vacuum on the lower port in the throttle body. If it does
not lose vacuum, look for a faulty fast idle valve on the
bottom of the throttle body, as long as the coolant hose is
good and hot.

Verify that the base idle screw was not turned way out on
the top of the throttle body. If it was, set the base idle
and see if the problem still occurs.

The upper port in front of the throttle plates feeds the
Idle Air Control (IAC) valve and the base idle screw. If
the IAC is unplugged and the base idle screw is turned all
the way in and there is still airflow through the upper
port, check for a stuck open IAC valve.