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2001 Honda Prelude Idling Issue

I need help with this one.
I got the car last fall so I don’t know too much of the history. I will list the symptoms the best I can.
-goes through about a quart of oil every 300 miles, looks to mostly come out the exhaust
-seems to really blow smoke when the vtec activates
-as the weather has gotten colder, it has been idling erratically until it warms up.
-check engine light went on today
-when accelerating from stop engine stutters briefly (this started when light came on)
-warm idle speed now seems to be over 1000 rpm
Any ideas? Please help!
5spd H22A4

I don’t even know where to start. Burning a quart every 300 miles and your title is about an idling issue.

The check engine light means there are error codes in the computer. Many auto parts stores read them for free. The format is “P1234” - have them read and post nothing but the codes.

How many miles are on it?

The check engine light stuff probably won’t tell you a thing about oil loss. Clean the entire PCV system and replace the PCV valve.

Do all of the basic “tune up” stuff - plugs & wires (if applicable) & filters. There’s no reason not to whether it does anything or not.

Before you go too far with time, $$, and effort you should probably check the compression and find out whether your should even bother with anything. The sensible time to do this is when you deal with the spark plugs.

Sounds like a beater.
Start with a compression test.
I’ll bet some idiot took the thermostat out and didn’t replace.

Error code P0505

An issue with your IAC (idle air control) valve. probably explains why it idles erratically, stutters until it warms up and idles too high. Maybe it just needs a good cleaning.

Here’s a pretty good description of the P0505 and this probably IS your idle and stutter issue. Note that it is a circuit issue (as so many codes point to), so it doesn’t mean “replace the idle air control valve.” It means first check the wiring for it, plug, harness, etc. If you can verify that the PCM is sending correct voltage and that the wiring contains no issues, then you’d assume the IAC motor itself is the problem.

This will not solve the oil consumption problem.

Honestly, I think the IAC problem is a result of the real problem rather than a cause. The excessive oil burning is, I suspect, because the engine is shot, probably due to poor maintenance, having run low on oil, and/or hard use (abuse). The carbon being produced is probably the root cause of the IAC problem. The erratic idling may be a combination of the IAC problem and uneven compression. One cylinder may be more worn than teh others, or even damaged.

Clean the IAC valve, but before sinking any more money into this I’d want to do a compression test. Post back with the results. I have a feeling that until you know the condition of the engine’s internals you’ll be chasing ghosts.

Very good information, thank you. I took out the IAC. Im not sure how to clean it though. It doesn’t seem to come apart very far. I do have access to a screen, which did have a fair amount of carbon on it which I cleaned. Do I need to disassemble it further? I think I would have to use some force to do so. Anyone know off hand what the correct voltage the PCM should be sending is? I’ll have to get back on the compression test, I dont have the stuff here to do it. But I imagine that will be quite informative.

Oh, when I took the vacuum hoses off of the IAC valve there was a fair amount of moisture that dripped out. Is that normal? And the car has 146k on it.

The carbon can be cleaned by spraking the valve assmbly off good with a cleaner sold in a spray bottle at the parts store that’s made for this. The counter guy can help you with the selection.

I don’t have access to Honda drawings, but perhaps the link I’ve provioded can help. It’s also very likely that a Google would give you detailed instructions on testing the IAC system.

Moisture is a normal component of exhaust. In addition to creating carbon dioxide, carbon monoxide, and nitrogen oxides, your engine creates water vapor. The gasoline has hydrogen atoms that get freed up, the air has nitrogen atoms that get freed up, and the two bond together to form H2O.

Cleaning the IAC is a must as long as you’re messing with it. But that code comes from incorrect voltage so you still need to check out the wiring & motor. I don’t know the specs. They should be in a repair manual. Probably resistance checks on the motor & basic voltage checks on the wiring.

Thanks for that excellent link. Guess I’m off to buy some seafoam. Man, I hope this works.

Just remember to not forget that you’re only curing the result of the base problem. You need to also do the compression test and evaluate the root of the problem…the excessive carbon. That’s largely what you’re seeing coming out the tailpipe. That’s largely what burning oil creates.

I think it may not be the IAC. If I unplug it the engine still idles erratically, just in shorter wavelengths. Then if I plug it back while the car is running in I can hear a gate open of some sort but the idle is not effected. Still in those shorter bursts. Its only if I turn the car off and start it again with it plugged does it do the longer revs. I checked the voltage going into it which ran at about 14v, and also the ohms out, which seemed to be in range as well. Im sure the engine is probably pretty close to shot. I’m just trying to buy some more time. The compression test has been on mind since long before this idling issue started. A couple of dollars on oil every two weeks is not so bad, right?

I like the way you think. But even though the root of the problem may be a shot motor, cleaning up the IAC valve can’t hurt. It might help the idle. Tough to say.