I did a radiator flush a while ago, and just got around to bleeding the system of air. While bleeding the system, the car was revving at 2000rpm. After finishing bleeding, i went to take the car for a test drive, and while driving around, the car sat at 1200rpm, and jumps up to 1600rpm, and drops back down, making the driving very unpredictable and dangerous.

After letting the car cool down, everything functions normally. However, after going for a drive (which brought the car up to temp), turning off the car to go in a store, and then coming back, the same symptoms happened again. The car shot up to 3000rpm in park, and when i put it in drive, it did the fluctuating rpm.

Any advice? Im thinking of readjusting the idle air screw.

 

Don't touch the idle screw... it was fine before. You still have air trapped in the system. You need to properly bleed it. Also, you didn't mention the model/year of the vehicle nor the engine code installed in the engine bay... and specifically, the intake manifold/throttle body combination being used. Does the throttle body have a FITV bolted to the bottom ?

 

Sorry. The year/model/engine is a 2000 Civic LX D16Y7 A/T. There are no codes present (other than a P0420, but thats due to a cheap ebay cat), and very rarely will a P0505 pop up (came up maybe once this year, and after clearing the codes has not popped up again). Intake manifold and TB are all stock. TB does not have the FITV (only in the Y8's i believe)

When i bled the system, i let it run for about 30 minutes. The bubbles slowly stopped popping up, but one bubble would come up every 5 seconds or so, but the coolant in the funnel stayed at the same level. Something I did not mention is after this bleeding, whenever I turn the car off after running it for a while, theres a slight hissing/gurgling noise coming from the passenger compartment (im assuming heater core?) The heat and A/C still work great, but if theres a pinhole leak in the heater core, could this be related to the bubble every 5 seconds when bleeding the system?

Thanks for your response, I look forward to hearing back from you.

 

DONT TOUCH ANY SCREWS. DONT ADJUST ANYTHING.

Ok, the gurgle you are hearing is air trapped in the heater core. The weird idle is air trapped in the intake manifold. Find a way to raise the front of the car as high as you can. I have a park in my neighborhood with a steep hill that I would park on. Once the front is higher than the back, pop off the radiator cap, start the engine. Let it warm up. When the thermostat opens, coolant will come out of the radiator neck. Why? because its pushing air out of the system. Once it stops burbling coolant slowly replace it. rev the engine a few times (about 2000rpm) once its warmed up. then let it run till the fan kicks on ( all without the cap on) When the fan turns off, put the cap on, and call it good.
Anytime you open the radiator, your gonna get air in the system, it just happens. Getting it out can be a big pain though

 

It is also worth a shot to confirm that ALL of your hoses that contain ANY coolant are double checked to ensure they're properly sealed/tightened. I went through a similar incident today. My car's issue involved a bad IACV, and lack of snug fitting clamps. I tightened the lines, bled the coolant in a similar fashion that .YOUSTOLEMYBEER, indicated. The problem diminished and the IACV was still acting up. I removed it and checked the ohm reading and it was less than when I received it from the carrier. I cleaned it out and replaced it with my OEM one and new seal. The car idles perfect now. You can adjust the idle screw, only if you know how to properly tune it. Let me know if you need more help. Best of luck, accelelag

 

Hi, responding as an update of my situation.

So the weird idle symptoms sort of stopped. Sometimes it'll kick up to 1500rpm while in drive and stopped (such as in traffic moments), but will stabilize after giving it gas and letting go at the right time.

I recently did a 200mile drive, and lost a bit of coolant. The overflow tank was way past the max line, and the radiator looked dry. I poured what was in the overflow tank, and it filled up to the radiator neck with a little under the min line left. While on my drive, the temp gauge shot up to just under the red line whenever I was stopped, such as at a stop light, but instantly went back down to the middle as soon as I started driving. I find it hard to believe that the coolant can get so hot so fast, and then cool down so fast as well. Any idea why that could be?

I've always suspected the head gasket to be leaking, as when bleeding the system, revving the car causes air pocket bubbles to shoot out of the funnel.

I just ordered the parts needed for a HG job. I was really avoiding this and hoping it was just a coolant hose leaking air into the system, but I may as well get it done. I'll report back after the HG job on how the car acts afterwards!