I have a 93 Honda Civic DX that has a problem which has me stumped. It seems that the idle might be a little too high and be causing this, but again, some things make me think otherwise.

When I slow down at a light and come to a stop sometimes the car will begin to vibrate quite hard and sometimes the rate of the vibration lessens, but the vibrations themselves get harder and eventually too great and the car shuts off.

The thing that makes me think that the idle is too high is because when I stop, the car sinks to the ground like it would if you tried powerbraking an automatic FWD, but my foot is completely off the gas. When I let off the brake to go, the car takes off at idle quickly.

Idle speed for the car I would say is around 10mph, but I have a worn speedo sensor that does not register up until ~20mph, so I can't say exactly.

I recently installed a new TPS which tested within spec, and was installed a .5V idle and 4.5V WOT per spec. I also cleaned the FITV valve thoroughly.
The radiator is quite rusty and I am sure that the block has a fair bit of the rust water corroded on it as well but I don't know if this would have anything to do with the way that it is running and how to clear most if not all of the rusty water from the block itself. I have heard of some people taking the water intake and running a garden hose into it and leaving the bottom of the block where it would flow into the radiator to cool open so it provides a constant clean flow of water. Tonight, I rose the front of the car using a ramp and topped the coolant off, turned the heat on high for ~15 minute at idle and let the engine warm up. Topped off the coolant again and then opened the purge valve. I had no air bubbles so I closed it and topped it back off, then lowered it.

Additionally, I do not believe the car has a thermostat. It cools quickly. Say, I idle in park on a summer day and I notice that the temp gauge is high, all I have to do is drive the car at a medium to hard pace and it drops the thermostat level down to near the C, which is where my car usually runs.

I believe I remember reading somewhere that the cars are coolant based, to say that the way the coolant runs through the block greatly affects the way that the motor runs.

 

Does the CEL work? Any CEL codes? Click link in my signature.

Have you cleaned the IACV on the throttle body?

Just install a thermostat. They're quite inexpensive.

If the engine overheats at idle, then check whether the radiator fan runs. If not, unplug the fan switch located on the thermostat housing and then jump the 2P connector with a piece of wire. If the fan now runs, then replace the fan thermoswitch.

Is your cooling system filled with water or 50/50 coolant? Why is there rust in the cooling system? Are you sure it's rust?

 

There are not any CEL codes coming through.

I recently cleaned the IACV/FITV, Installed a new TPS and calibrated to .5V @ Idle, and 4.5V @ WOT and bled the coolant system.

I'm 100% positive that it's rust.... unless you can tell me of another red grainy substance that builds up in an aluminum radiator...

It has 50/50 since I dropped some of it, but I couldn't figure out how to remove it so I could not do a proper flush of it.

 

Does the CEL work? When you turn the key to ON(II), does the CEL turn on and then off after 2 seconds?

If you remove the intake and then cover the top of the throttle body with your hand, are you able to kill the idling engine?


Click here to learn how to flush the cooling system. So the engine has been run for some time on water rather than coolant? Sometimes a blown headgasket will allow oil and exhaust gases into the cooling system and this will discolor the coolant.

 

Yes, the CEL works. It told me that I had a bad TPS (Code 7) and once the TPS was replaced, and the ECU reset, the code was removed. I have no idea if covering the TB will produce this result.

 

If you can't kill the engine by covering the top of TB, then you have a major vacuum or intake air leak, which can cause a high idle. Another possible cause for a high idle is a throttle cable that is adjusted too tightly (should have 1/2" free play) or a dirty TB. In these cases, the throttle plate is held open even when the throttle pedal is not pressed.

 

I can kill the car by covering the TB.