Ok it is a 90 civic w/ a z6 and pm6 ecu. It drives fine, but as soon as he puts it in neutral the rpm's go from like 1800 down to 800 then back up to 1800 then back down, get it? What could the problom be? And how can we fix it?
Thanks

 

i asked this question before cuz i have the same problem. what people told me was the 02 sensors that were going bad.

Jeff-

 

if the idle is goin up and down try you EACV .. its a valve on the back of intake manifold. could also be your dizzy . do you have codes like maybe crank angle sensor?

 

aim- pkbjoonho

 

Ok this maybe of no help at all because they are different cars, But I have a 1988 Honda Accord DX HB as a winter beater and I have this problem also. The only difference is that mine idles high around 2200 RPM and it will drop down to 900 RPM or so and it will do it off and on at any given time. Well anyway, I brought my car to the Honda dealer and they told me that it is a bad ECU that is located under my drivers seat. One other side effect was that anytime I turned on my air conditioning it would idle at almost a stall if the RPM's were not already high. One other thing that is closer to your problem of your RPM's consistantly going up and down was a 1986 Honda Prelude Si which ended up being a vacuum leak. Hopefully some of this info can be of some help.

 

vacuum leak.. or reset your ecu..

 

coolant leak, could be possibility..

 

cool, i'll check his ecu and coolant. and get back to you.