91 civic idles high & low in neutral
 

my 91 honda civic idles high and when I push the clutch in to stop the engine revs up then down constantly until I push the gas to move. It dont do this until I have drove about 2 blocks then it starts. Also when I push the clutch in after it is warmed up, the engine races badly (only when the clutch is pushed in). I have cleaned the IACV and filled all the fluids. This is realy sucking the gas with the engine doing this. Can someone please give me some ideas? Thanks.

I'm not sure if your car has a fast idle valve (FITV), but if it does, that's where I would look.

it can also be the throttle position sensor(tps) its on intake mani has three wires goin 2 it
green,yellow,red

do you have the dpfi or the mpfi???

Is the LED on the ECU blinking a code?

Have you checked for a leak from a vacuum hose?

Have you tried to adjust the idle speed with the idle adjust screw on the throttle body?

Unplug the IACV connector. Do you measure 8-15 Ohms across the two IACV terminals?

I have no idea if their is a fast idle valve or not. before I got the car someone put a racing mufler on it. I dont know about the engine other than it says 16 valve Honda Motor. I took it to a garauge but its too old to hook to the diagnostic machine so they had no way to help me. My husband says that it has a throttle body in it (if that helps).

Are you able to answer any of the questions in my previous post?

Do you have a 1.5 liter or 1.6 liter engine?

I don't think your engine has a fast idle valve.

No need for a scan tool. Your Civic has a self diagnostic system:

Attachment 18667

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ok I found the LED display and it is blinking 1---1---1---1. What is it?

Code 1. It indicates a problem with the oxygen (O2) sensor or its circuit. This sensor provides crucial information used by the car's computer (ECU) to determine the correct air:fuel ratio for combustion. This sensor is needed for optimal engine performance but is unlikely to be the cause of your idle problem. First remove the HAZARD fuse in the main fuse box for 1 minute to clear the ECU. If code 1 does not return, then do nothing with the O2 sensor.

Do you have a 1.5 or 1.6 liter engine?

Focus on the other items that I mentioned to troubleshoot the idle problem.

Here are the vacuum hoses (1.5 liter engine) to inspect for leaks:

Attachment 18666

well I have a NEW o2 senser and cleaned the IACV and then removed the HAZARD fuse and replaced it.(didnt notice to do that first, lol). The code 1 did not come back on but the engine still idles high then low then high & low when the clutch is in (in neutral). We cant find any leaks. I realy like this car but the constant reving high & low is just too worrysome to drive. I am leary of putting my kids in it untill I know what is causing this. how can I know what size the engine is when their is nothing under the hood that says 1.5 or 1.6?

Is the resistance 8-15 Ohms across the two terminals of the IACV?

Is the coolant level low? Have you tried bleeding the cooling system of trapped air? If the coolant system is full and bled, then check whether disconnecting the thermosensor eliminates the hunting idle.

Attachment 18649

What's the engine number?

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