extremely high idle speed

1995 Eclipse RS no turbo 2.0L

My idle was fluctuating between 1200 and 1800 rpm so I took the IAC out (located directly below the TPS) and cleaned it and the air intake throat with carb cleaner. Put it all back together and checked to make sure everything was hooked back up. The car will start immediately, but the idle now goes to 4000 rpm and holds steady.

What's up with that?

Here is what I found when I took the IAC back off...

It had not extended at all. It was completely open allowing max air flow...causing high idle rpms. Now the question is why wont it extend...

I cant pull the tip out physically and when its plugged in it wont extend. The tip does however screw into the IAC module. I can unscrew it and make it longer (extended), but I dont think its suppose to be that way.

I tested the four prong connector going to the IAC using a multimeter. I grounded the black (ground) end and turned the ignition to the on/run position. Three prongs tested around .08 volts and the fourth prong tested at .28 volts. I then applied 12V from the battery to the IAC itself going from one prong to another, one at a time to see if the tip would extend....nothing happened.

So....have I tested the IAC and connector correctly? What else should I do or check for before condeming the IAC?

I don't know anything about the 2g NTs, but try resetting the ECU, then watching the ISC the first time you turn the key to the on position. On the turbo motors it will extend fully and retract as it runs through it's home/sync sequence. All stepper type ISCs should do something similar after an ECU reset.

1995 Eclipse RS no turbo 2.0L

My idle was fluctuating between 1200 and 1800 rpm so I took the IAC out (located directly below the TPS) and cleaned it and the air intake throat with carb cleaner. Put it all back together and checked to make sure everything was hooked back up. The car will start immediately, but the idle now goes to 4000 rpm and holds steady.

What's up with that?

Also, how much carb cleaner did you use?

I used about 1/2 of a can spraying it down and cleaning the carbon build up off of it and the throttle body where it inserts. It and the throttle body was really dirty with carbon build up.

As for resetting the ECU.....is there a fuse I should do that with, or disconnect the + battery cable?

Is IAC and ISC the same module?

I used about 1/2 of a can spraying it down and cleaning the carbon build up off of it and the throttle body where it inserts. It and the throttle body was really dirty with carbon build up.

As for resetting the ECU.....is there a fuse I should do that with, or disconnect the + battery cable?

Is IAC and ISC the same module?

Are you sure it's completely dry before you put it all back together?

Pull the negative battery terminal for a couple minutes.

Ours are an IAC... but pretty much the same thing. The ISC I believe it a little more complex.

Yea they are both the same thing. Disconnect the battery a few minutes and that should reset the ECU.

I disconnected the - battery cable for a couple minutes. After hooking it back up, I turned the key to the on/run position and looked under the hood at the IAC module. It did not move at all. I do not have the IAC in the throttle body, it is just sitting out while plugged in.

As for the question of "was it dry when I put it back in"......more or less. It wasnt dripping wet.

THROTTLE BODY MINIMUM AIR FLOW CHECK



Start the engine and warm it up until the engine coolant is heated to 80°C (176°F) or higher and then stop the engine.
Remove the air intake hose from the throttle body. http://www.alldatapro.com/alldata/PRO~V96311173~C21223~R0~OB0~P3R0H~N/0/41746505/56622862/56622865/56622867/34853741/34857029/34858641/58800534/58059549/86203402/41793546



Disconnect the Positive Crankcase Ventilation (PCV) valve hose from the intake manifold nipple.
Attach Air Metering Fitting 6457 (0.125 in. orifice) to the intake manifold PCV nipple.
Disconnect the 3/16 inch idle purge line from the throttle body nipple. Cap the 3/16 inch nipple.
Connect the scan tool to the data link connector.
Restart the engine. Allow engine to idle for at least one minute. http://www.alldatapro.com/alldata/PRO~V96311173~C21223~R0~OB0~P3R0H~N/0/41746505/56622862/56622865/56622867/34853741/34857029/34858641/58800534/58059549/86203402/41793547



Using the scan tool, access the SENSOR READ TEST "Minimum Airflow Idle Speed" screen.
The following will then occur:
Idle air control motor will fully close.
Idle spark advance will become fixed.
Scan tool displays engine speed.
If idle RPM is within the range shown in the chart below, throttle body minimum airflow is set correctly. Standard value: 550-1200 RPM (Less than 1000 Miles) 600-1200 RPM (More than 1000 Miles)
If idle speed is not within specifications, shut off the engine and clean the throttle body as follows:
Remove the throttle body from engine.
While holding the throttle open, spray the entire throttle body bore and the manifold side of the throttle plate with cleaner. WARNING: Clean throttle body in a well ventilated area. Wear rubber of butyl gloves, do not let cleaner come in contact with eyes or skin. Avoid ingesting the cleaner. Wash thoroughly after using cleaner.
Using a soft scuff pad, clean the top and bottom of throttle body bore and the edges and manifold side of the throttle blade. The edges of the throttle blade and portions of the throttle bore that are closest to the throttle blade when is closed, must be free of deposits.
Use compressed air to dry the throttle body.
Inspect throttle body for foreign material.
Install throttle body on manifold.
Repeat steps 1 through 14. lithe minimum air flow is still not within specifications, the problem is not caused by the throttle body.
Shut off engine.
Remove Air Metering Fitting 6457 from the intake manifold PCV nipple. Reinstall the PCV valve hose.
Uncap the throttle body idle purge nipple and connect the idle purge line.
Remove the scan tool.

That is some really detailed diagnostics.....unfortanately, I dont have a "air metering fitting" or "scan tool".

About the best thing I can do at this point is purchase another IAC over the weekend and put the throttle body back together. Hopefully that will resolve my issue.

I forgot to mention.....while cleaning the air intake manifold with carb cleaner, the pipe coming from the EGR valve and connecting to the air intake manifold was really clogged. I cleaned it with a screwdriver and carb cleaner, but I believe quite a bit of carbon build up got into that line. Once I start the car with the new IAC, will most or all of that loose build up blow thru the air intake and out the tail pipe?

I forgot to mention.....while cleaning the air intake manifold with carb cleaner, the pipe coming from the EGR valve and connecting to the air intake manifold was really clogged. I cleaned it with a screwdriver and carb cleaner, but I believe quite a bit of carbon build up got into that line. Once I start the car with the new IAC, will most or all of that loose build up blow thru the air intake and out the tail pipe?

That pipe usually gets clogged pretty quickly. It will get sucked into the motor and pass through. Just make sure that the EGR pipe is passable. It won't cause any big problems, just will throw a CEL and cause some crappy idle/gas mileage. But since it's off or nearly off, clean it out anyways.

How long have you ran the car? Maybe it just needs to idle high for a minute and let the IAC find its position. I would crank it up and let it idle that high for a minute or two and see if it comes down.

How long have you ran the car? Maybe it just needs to idle high for a minute and let the IAC find its position. I would crank it up and let it idle that high for a minute or two and see if it comes down.

When everything was together and the idle speed was at 4000 rpm, I let it run for about 1 minute. The idle speed never went down and never acted like it wanted to. Letting it idle at that high of rpm's for more than a minute is dangerous to my engine (it has high mileage).

ISC and IAC are just different acronyms for the same part. If it didn't move when powering up the ECU for the first time, I have to assume the ISC motor or the ECU's driver is dead.

ISC and IAC are just different acronyms for the same part. If it didn't move when powering up the ECU for the first time, I have to assume the ISC motor or the ECU's driver is dead.

How would I go about checking the "ECU driver"?

Easiest way it to just swap in a known good ISC motor.

were there any codes when this started or the mil on?

were there any codes when this started or the mil on?

There was no check engine light on at any time during the entire process.

Well.....bought the new IAC and installed it today. IDLES LIKE A NEW CAR :smile:
It was a bit expensive for my low budget taste, but gotta do whatcha gotta do. Thanx guys for all the assist.