Topic: 1991 Accord Erratic Idle

[campbmic]

Hey guys Ive posted this on a car site and havent gotten any response was wondering if any of you guys knew what was going on.

I bought a 91 Accord EX Station Wagon at a police auction a few months ago. Put a new battery in it and it started right up. The only problem is the idle instantly shoots to 3k then drops to 1.5k then shots back up to 3k and drops. This is just constantly going on the entire time. Like a ghost is revving the car haha.

Anyways, aside from a exorcism what else could fix this?

[Roach]

Have you ever tried to look at your PCV valve? Are you familiar with it? If not, this device is a one-way valve that ensures continues flow of air inside the combustion chambers. Positive crankcase ventilation or PCV valve as it name implies is found on the crankcase of your engine. That�s actually one part of the PCV system which is vital in the operation of your engine. Nevertheless, like all other auto parts, this valve wears out over time since it is always exposed to massive pressure that is given by the air intake system as well as to the excessive thermal energy created by the engine during the power generation. If this starts to fail, some of the flow of air will be going back to the intake system. Subsequently, only a lesser amount of air is permitted inside the combustion chambers. The negative effect of such condition will also be felt with rough engine operation.

so try your pcv valve!! mine went in my 90 integra and did the same thing

[Gordon]

Check for vacuum leaks.  Is the "Check Engine" light on?

[scottly]

If I recall correctly you had a similar problem on your trip to NY(?) last spring, and I reported a similar problem with my '01 Civic. While looking through my manual for something else, I stumbled on a section about "re-teaching" the computer how to idle the motor, after the battery had been disconnected. The other EFI cars I have worked on taught themselves, after a short period of driving, but the manual for the Honda called for a specific procedure. I haven't tried it yet, as it isn't that big of a deal at this time. I've been much too busy getting ready for the RELAY!!!

[Cbowers]

I think this is caused by a faulty Idle Air Control Valve. I believe you can clean them. I think it is on the oposite end of the intake manifold from where then "intake" is. you may want to google that though it has been a while. I have a buddy with an mid 90s integra that did the same thing.

[number13]

On modern (after 1980) cars I have found two things
that cause these types of problems, the throttle position
sensor and the crank position sensor. Have they been changed
recently?

[Really?]

I have read on an explorer forum that one guy had something jacked up in the trans which affected the signal to the fan clutch that sent the wrong signal to the IAC.  Not saying this is the case though.  Crazy.

[fmctm1sw]

I think this is caused by a faulty Idle Air Control Valve. I believe you can clean them. 

+1.  I had to do this on my 93 Dodge van a while back.  Put it in gear and it would stall.  About 30000 miles of good operation after that but it's starting to do it again..

[Really?]

You might be able to spray plenty of electrical cleaner or MAF sensor cleaner in there and let it soak a bit.  A lot of peeps do that.  I have done it and used the MAF cleaner.  I need it to clean the MAF at each air filter change anyway.

[apex_seeking]

Had this happen on my 95 civic. It ended up being a faulty ignitor under the cap. Replace the plugs, cap, rotor and the ignitor and you should be running a lot better.

[DH]

iirc, some of the old hondas had some type of fast idle control valve that worked much like an engine thermostat. The valve was located in a coolant passage somewhere in the intake manifold. As the coolant warmed, the valve responded and cut airflow, slowing fast idle. When this valve malfunctions, it acts like a bad thermostat would, rapidly opening/closing, causing the idle to surge constantly.
Not 100% sure if the hondas had this set up, but you could research it...

[scottly]

From the Chilton manual for '01-04 Honda Civic & CR-V:

When the battery is disconnected.. it is imperative that you perform the "PCM idle learn procedure

1. Make sure that all electrical components (air-conditioning system, lights,rear window defogger, sound system, etc.) are turned OFF.
2. Start the engine, bring it up to 3000 rpm and hold it there, with no load (in PARK or NEUTRAL), until the radiator fan comes on, or until the engine coolant temperature reaches 194-degrees F.
3. Allow the engine to idle for at least 5 minutes with no load on it and the throttle fully closed.

Note: if the radiator fan comes on during this five-minute period, don't include the time during which the fan runs as part of the five minutes.