I have a '98 Civic sedan that I just replaced the engine in, from a D16Y7 that spewed oil out of the exhaust to the tune of 1qt every 300 miles, to a lower-mileage junk yard motor that ran great in the car I pulled it out of. The swap went smoothly enough, considering it's my first, but now I'm having issues: I'm getting the infamous P0505 code and the car is pretty much undrivable. "Clean the IACV", you say. Well, I tried that. And it didn't work. And then I replaced it with the one from the other engine. And that didn't work. Then I cleaned the replacement. Still doesn't work.

Here's what happens:

I go and start my car (cold). Starts up fine, settles into a 1000rpm idle, which seems normal for a cold engine.
Drive for a bit, all is well. Acceleration is smooth, smiles are on everyone's faces.
Come to a stop, and I'm warmed up but idling at 1000 with it bouncing up 100rpm like a weird-*** lumpy cam. Take off and start driving and the first 20% of my throttle just makes the bounce more intense until it finally takes off. If I'm in gear with the clutch out and I go below 1700rpm the entire car shakes (like a slipping clutch sort of thing) to the point my girlfriend hit her head on the dashboard.
Turn car off, turn car back on, 500rpm idle, all is well... for a random amount of time, then it all starts again.

My only thoughts are:
Cooling issue, which doesn't make much sense because coolant is flowing through just fine, as evidenced by how much sprays out when I undo the cooling lines.
Something wrong with the throttle body that keeps making my sensors bork up. I have no idea what this could be, and I'm hesitant to replace TBs because the gaskets are super touchy.

Thoughts?

 

air pocket.

 

When you did the IACV did you reset the ecu? Also clean and adjust FITV.

 

Best place to start^

Properly bleed and go from there.

 

I'm gonna sit back and let you think about what you posted here before I start berating you.

 

Reset the ECU? I unplugged the battery for about a half hour and cleared all codes, if that's what you mean. I would adjust the FITV, but my car doesn't have one.

Ok, I'll try that tomorrow, though I'll admit to not really understanding how air in the coolant system affects this sensor. Does it just overheat and shut down?

 

I cleaned my IACV 2 months before I got code 14 for IACV had the same jerking within the 1100-2000k rpm range op has, cleaned the IACV and set the FITV all the way down that fixed my code and the issue.


Just noticed he's obd2 hey no flames.

 

Long story short, if there's an air bubble in your system, it'll find the highest point in the system, which is the IACV. IACV + air = "failed" IACV, as far as the ECU is concerned.

People wanting to help is always good. I might give you a lot of **** in GDD, but if you stay around tech long enough, you'll see that I have a different personality in tech than in GDD. That said, what good is expecting people to list all vehicle information if people trying to help aren't going to pay attention to it? Just gotta keep up with that stuff when you're trying to help, or best case it defeats the whole purpose, and worst case it confuses the everliving **** out of everyone.

 

Actually, bubbles cause idle problems because they interfere with the ECT sensor's ability to read coolant temp correctly, thereby misinforming the ECU about how it should control the IACV.

 

Honestly, I've heard it both ways, and both ways make sense. But yes, an air pocket can also get caught at the sensor, giving it false readings.

 

Are you aware that the only function of coolant flow through the IACV is to prevent Canada-type winter conditions from freezing it up? Otherwise, air in the IACV coolant hoses would have no effect on function.

 

Really? I could have sworn it had something to do with the actuation of it, too. Eh, I've been wrong before, it happens

 

Will defenitelty pay attention to that more. And yeah noticed here youre more calm, cool and collective lol.


OP when you rev the engine and hold it at a steady rpm does it stutter/bog?

 

No. Once I get it over 2.3k or so it's just fine. Only when I'm at idle or driving around at idle speeds or letting off/coming onto the gas while driving.

 

Well, that didn't work. I tried bleeding the system and successfully got a lot of bubbles out, then the IACV code got thrown again and my car became virtually undrivable on my way home. I have no idea what to do at this point. This is the IACV off of my old known-to-not-have-this-issue engine.

 

What is the actual code?

 

D0505.

 

Do you mean P0505? Is that the ONLY code being thrown?

 

Yep, P5050 is the only code. I'll check out that flowchart, but I've replaced the valve before to no avail. Maybe I could use something to clean out the throttle body? It idles at 1.5k when warm...

 

Closely follow the troubleshooting procedure in the flowchart based on the specific type of idle problem you have, which takes you on the (B) branch.