Rokura

I was doing some maintenance on my wife's car and noticed a problem with high idle. Her sister borrowed the car for several months and we got it back needing a new water pump, which i replaced when we got it back. I noticed that it idled high even on the way back. We started it to make sure it ran then turned it off before driving back to our house. In the past I did not pay much attention to any problems with the car because she always had a mechanic do repairs. I don't know if the high idle occurred before or after the water pump going bad.

I have a b18b1. From cold start, the engine idles around 1500 rpm during warm up. Once warm it drops to around 800-820 rpm. It does not surge or hunt when cold or warm. The engine will continue to idle around 800-820rpm. If I turn engine off and then back on within a minute, it then idles around 1500 rpm. I let it sit off for 20 minutes and then warm up again but the car will idle warm at 1500 rpm. I let it cool completely and checked again a few days later. The same thing occurred...it idles 1500 during warm up then drops to 800-820 without turning engine off. Once engine is turned off then restarted within seconds, it idles high around 1500.

All engine and transmission mounts have ben replaced but the car does have a small vibration when it is idling. The vibration has been there for as long as i can remember.

No check engine light (CEL)

I have already done the following:
- Checked for vacuum leaks around the intake.
- Cleaned idle air control
- Disassembled and cleaned all of the fast idle thermo valve (including the coolant side) and then reassembled. I made sure to tighten down the white plastic collar.
- With air intake hose and filter off, I plugged fast idle thermo valve hole in throttle body in case there is any air flow. No change to idle.
- Adjusted engine valves/rocker arms
- Rechecked firing order, plug wires and spark plug gap
- Inspected checked plug wires for cuts and measured resistance/ohms
(the plugs, rotor and cap replaced within last few months but car was mostly sitting)
- Bleed air from coolant system after replacing timing belt, water pump, radiator hoses, thermostat and coolant flush with running water hose
- Cleaned throttle body
- Checked throttle cable. The cable is not binding. It is also not keeping the throttle body butterfly open when idle. Air flow through the idle air control solenoid instead.

Any suggestions for what is causing this?

wunfstgsr

ECT sensor may be faulty. And or your IACV is bad.

Rokura

Thank you wunfstgsr. I finally got it fixed. The Engine Coolant Temperature (ECT) Sensor was bad.
It took a while because I was traveling for work. I also had to return a new ECT because it looked used; the o-ring was damaged and melted to the ECT and threads were very dirty. I did not want to put a bad or used ECT when I paid full price.

I tested once at room temp and then with warm water, both results showed a good ECT. My second test showed it was bad. The difference of the first test and the second is that I watched the meter reading for a longer time during the second test.
At room temperature, it had the correct resistance around 1.5k ohms).
I then put it in some hot water around 120 degree Fahrenheit. When it started to warm up in the water, the resistance was dropped to around 0.980k ohms then spiked up to 430k ohms. An hour later sitting at room temperature, it raised to over 500k ohms.

Lesson learned: conduct test at least twice and watch the meter closely.

wunfstgsr

Good to hear! and that you fixed the problem! I wonder how they sold you that sensor in that condition lol