Honda engine idle roaming

My 91 Honda Accord has an engine idle problem. A minute after cold start or when I take the car out of drive, the engine idle roams up and down. Mechanic suggested a low coolant problem, which I fixed, but the idle problem remains

Look for a vacuum leak. If that does not help, then the IAC motor is likely to be the source of the problem.

I can’t add anything to VDCdriver’s post, other than to tell you IAC stands for Idle Air Control.

I had a similar problem with my '88 Honda Civic WGN, 5 spd 1.6L. I checked many things which I thought might contribute to the problem, especially vacuum leaks. The folks at my local Honda parts counter suggested changing a temperature sensor on the driver’s side of the block that inputs engine temperature to the computer. This solved my problem after many, many times trying to locate the cause.

Drive safe!

Captain Jack

Thank you. I’ll see what I find when I work on this tomorrow. The Honda manual suggests the possibility of a bad egr valve or solenoid which could cause a vacumn problem.

Here is the location of the engine coolant temperature sensor (ect):,4294963501/shopping/locsSelect.htm
For the removal of the the ect, the repair manual will instruct you to drain the cooling system down a certain amount. This isn’t necessary, as only a cup of coolant will flow out before you can install the new ect. Lah peek*chur:,4343195/vehicleId,1608701/initialAction,partProductDetail/store,1140/partType,00113/shopping/partProductDetail.htm