High/Low idle

ADAM SAPERSTEIN

MEMBER
HONDA ACCORD

I have a 1997 Honda Accord - 2 WD, 4 cylinder engine, 121,000 miles. Over the last week, when putting the car into park after driving, the car will idle high and low going back and forth over and over. If I put the car into gear, this stops. If I put the car into gear and then back into park, it also stops. If I drive a ways and then park again, it starts again. This does not happen when I first start the car. I have watched this happen and looked at the cables for the accelerator in the engine and the cables do not move when this occurs. What is the fix? Thanks.

3 Replies

BRUCE HUNT

MECHANIC
3,753 POSTS

I call this surging and it can happen all the time, only when engine is cold, or when the engine is warm. Yours appears to be only when warm. Here is a list of things to look for:

vacuum leak - could be a hose cracked, broken, or loose
bad or plugged IAC valve - the Idle Air Control valve can be taken off and cleaned
air in the cooling system - with the engien warm crack open a bleeder on the cooling system (antifreeze not freon) Remove the air from the system. A possible leak in the system could be allowing air in.
Check the EGR valve
bad O2 sensor
bad MAF sensor

Start at the top and work your way down.

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Wednesday, July 18th, 2007 AT 8:31 AM

ADAM SAPERSTEIN

MEMBER
2 POSTS

Bruce - Is there a reason why it does not happen when the transmission is engaged or the car is in neutral?

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Wednesday, July 18th, 2007 AT 8:59 AM

BRUCE HUNT

MECHANIC
3,753 POSTS

I am not sure why it fails to do it when in neutral, but generally it does not do it when the vehicle detects a load. What I know is that you have a sensor that is reporting bad information. The ECU tries to compensate for the information it is getting and it is wrong. So, that said, the sensor at fault is either failing to pass on good information or is gathering bad information. For instance, the temp sensor located by the thermostat could have a pocket of air sitting on it and thus the sensor is not able to read correctly the temp of the engine. It can just be a failing sensor as well.

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Wednesday, July 18th, 2007 AT 11:31 AM