blkspd5

Hey guys, I've been doing a lot of searching around and can't seem to find out why I'm having a weird idle issue. My problem is a low idle bounce in gear after coming to a stop. Initially the car started to stall/die at idle and I changed the distributor and it hasn't died since. I also adjusted the base idle timing to withing spec. The car idles perfectly right at 700 RPMS while in park with lights/heater/ac OFF. But whenever I drive and come to a stop it will idle down to about 500 RPMS, then jumps back up to 700 and idles back down repeatedly. So I initially thought the IACV was dirty, so I cleaned it and the TB with zero luck. I kept reading when you unplug the IACV you should idle at base idle around 450 RPMS. Well mine idles at 1500 RPMS with the IACV unplugged and sounds like its bouncing off redline. I tried to adjust the idle screw, I turned it fully in and fully out and it did not change RPMS at all. So I went to a wrecking yard and found another TB with everything on it, except the MAP sensor. I cleaned it up really good, swapped the MAP sensor onto it and I still have the same issue going on. What could cause the idle to be so high with the IACV unplugged?

I've done the following things, some maintenance and some trying to find the issue;

2000 Civic EX A/T D16Y8 w/ 110k miles
-Timing Belt & Water Pump
-Valve Adjustment
-Plugs, Wires & Distributor
-All Belts
-Air Filter
-Oil Change & Transmission Flush
-Coolant Flush (I made sure it was bled)
-Cleaned TB, IACV
-Replace TB
-Searched for Vacuum leaks

09chaplak

So this only happens when you're in drive and not in park?

mk378

Unplugging the IACV is only applicable to two-wire IACVs. Your automatic EX would have a 3 wire IACV.

False cold readings from the engine coolant temperature sensor will cause the ECU to command a fast idle. Check that cooling system is full. Check ECT sensor with ohmmeter or reading live data by OBDII scanner.

Check the FITV on the thermostat housing for broken plastic or disconnected hoses. Check that you can stall out the engine by blocking the air bypass holes in the side of the throttle body before the throttle plate. It can only idle fast if air is getting in somehow.

b00b00559

My 95 civic does the same and I cant figure it out. When I had bought the car the idle would go up and down like crazy so I replaced the IACV and it fixed the problem. This was in winter and now that its warming up after driving it a little bit the idle will jump up and down at a low idle (450-800) up and down rapidly when I stop. After about a min it will stop and go back to normal. Then it do the same once i stop again.

blkspd5

blkspd5

mk378

Have you set the timing with a timing light? Are there any codes set?

I would try opening up the air screw as much as you can until it starts going too fast in neutral.

blkspd5

b00b00559

I need to make a video of mine so you can see what mine does.

civic402lx

Have you try a new thermo switch sensor? The sensor that is below the distributor.

09chaplak

When bleeding, squeeze the lower hose a little bit.

civicservice

What do your short/long term fuel trims look like?

mk378

Also when you have an OBDII scanner, watch the ECT reading. On a cold start it should start at about the temperature of the place where the car was parked. Then it should warm up to about 190 and stay steady. Fluctuating readings from the ECT sensor will cause idle speed to fluctuate.

blkspd5

blkspd5

crazyhorse2011

OP invest in a bluetooth OBD2 scanner. Use torque lite app on your phone. Mount your phone up in the windshield and watch the parameters. Engine coolant temp. If its erratic, replace sensor mounted below the distributor, its like 20 bucks and 3 minutes of labor

blkspd5

blkspd5

-I haven't noticed any fluctuations lately, but I did however notice my avg. mpg for last tank was 22. I put some Lucas fuel system cleaner in and did a lot of idling/testing so maybe that's why. Just filled up again so I'll see how this tank does.

-ECT readings have been spot on, slowly will climb to when the fan kicks on at idle and then back down. No jumpy numbers.

-I swapped in my original cleaned throttle body today. I noticed my idle would drop coming to a stop to about 350-450rpm, so I turned the idle screw out a bit like I did with the other throttle body from the junkyard and it seemed to be fine. Idles around 650-700 while in "D" at a stop now. I also checked the TPS Voltage at idle and I was right around .49 which seems close enough to where it should be at. The stock idle screw position was about 1/2 turn out from being turned all the way closed. I had to turn it to 1 1/2 turns out from being turned all the way in to get the idle to not bog down so far. What is the normal position the idle screw should be at?

-Thinking at this point I'll just drive the **** out of it and wait for something to happen?

blkspd5

mk378

Whenever someone with a 6th generation says their lights are flickering, you have to think fuse 15.

Through all of this, no ECU codes and no CEL? Check that your CEL works by turning the key on but don't start.

crazyhorse2011

Clean your ground wires really well.sandpaper the mating surfaces

SportsFan

Is it required to drain the antifreeze from radiator prior to changing this temperature sensor? Thx for your info!

SportsFan

An update to my earlier post - I did flush my antifreeze and then made sure to take all those crazy bubbles off by using a big funnel onto radiator and letting engine warm up as I topped it off. Things came back to normal. Also make sure the IACV is the accurate one - there are 2 kinds: one for automatic transmissions and one for manual. They both look somewhat similar but different mechanism.