I don't have any CELs

Problem 1:
When I show down and put the car into neutral or down shift the RPMs go to 500 and then quickly back up to 1000. I notice this mostly when I'm in the higher gears. I thought it was the TPS, so I replaced it with a used one. Ohms tested out okay. 0.5 ohms at closed and 4.5 ohms at WOT. However the problem still occurs.

Problem 2: The RPMs will jump as bad as 900-1400 but usually closer to 1000-1300. This happens on a few different occasions. Mostly when rolling in neutral. It's not regular. If i brake hard to almost a full stop it can set off the rolling RPMs. I feel like the lights are somehow tied into this because I notice it mostly when I have the lights are on. Also, the car will idle at about 1100rpms with the lights on. When I come to a complete stop and turn them off they will go to about 650RPMs. Then if I turn them back on the RPMs will go to 800ish. Once driving again for a little while the RPMs will be back at 1100 when in neutral or at a stop sign/light

There has to be a vacuum leak somewhere right? I can't locate it. I've pulled off the intake and put my thumb on the IACV port and the engine turns off. I also ran an unlit torch (propane) around the vacuum lines but there was no change in engine noise.

Problem 3: The car also seems to take a long time to warm up. 1500 RPMs when first turned on, and it will stay there until about 10 minutes of driving. Its fine if I'm in gear, but when I'm stopped at a light the RPMS are just at a steady 1500. Thought it was a temp sensor, or thermostat but the heat blows hot enough, and the temp sensor reads in at about 8:00 or 8:30. How long is it supposed to take for a car to warm up? RPMs at 1500 for 30 - 90 seconds is fine, but 10 minutes is a little much.

 

Remove your IACV and clean it. Sounds like it is sticking.

Then if there's still a problem, try opening the air screw some. That is the big flat head screw in the top of the throttle body. Do not adjust the little screw that stops the throttle plate. With the IACV completely closed (if it's a 2 wire type, unplug the wire) or blocked off, the engine should still barely keep running on air from the air screw.

 

I tried this earlier. When I open the air screw past a certain point the RPMs start to jump up and down in the same way that they would with a vacuum leak. This is with the IACV still plugged in. I haven't tried this with the IACV unpluged yet. I don't know if I want to because my Idle is set up just where I want it.

 

If the IACV is working properly, it doesn't matter too much how the air screw is set. The ECU has hard-programmed control of the idle speed, it will resist attempts to "set it right where I want it."

If the engine idles too high after warmed up, but slows down when IACV is unplugged (2 wire type), the ECU could be thinking the engine is still cold due to faulty ECT sensor. This does not necessarily throw a code, if the sensor is not so far out of line that it is still in limits to not throw code. Test ECT with an ohmmeter or if you have an extra one around swap it out.

Also make sure the cooling system is completely full, as bubbles of air in the engine will cause an unsteady idle.

 

If that's the case, then it sounds like my IACV isn't working correctly. If I turn the screw to much, the rpms surge up and down. Or is that normal? Turns out I didn't have all the air out of the system. I just spent about 30 minutes messing with the bleeder screw. Lots of tiny little bubbles. I'll check again tomorrow after I drive around to see if there's still air in the system. This is the 3rd time I've bleed it. I might have a leak somewhere, but there isn't any coolant on the driveway or anywhere that I can see in the engine.

 

I am having a similar issue with my 99 Civic. It takes a while to get up to temp, but runs fine for a time. After driving for 30 to 40 minutes, the rpm's while slowing or in neutral drop to around 500 or less, eventually the engine dies & will not start again for a day or two. It's gotta be something electrical that's overheating? I get no overheat reading on the temp gauge in the car. The car has now stranded me twice, very frustrating.

 

Excuse my ignorance, but what is an IACV?

 

I have the exact same problem as above it has been happening for three weeks tested battery and alternator multiple times passed with flying colors. I have no idea the only thing i can think of is the eld electrical load detector. Does anyone know if im guessing right?