I'm in the process of figuring out a confusing issue and hope to get some input as I prepare to troubleshoot. I'm not expert, but I have a decent understanding of engines and I've done a bit of research on this.

2000 Honda Accord Ex 2.3L Vtec 4 cylinder, 5spd, 116,000 miles

I bought the car last week and immediately drove it on a long trip. No problem for first 200 miles. Suddenly began to run poorly under load - felt like misfiring with a low rhythmic thumping. Immediately stopped to check it out. Found PCV breather (that's the hose that connects the valve cover to the rubber intake tube - left arrow in image below) had become disconnected from the rubber intake tube (connection out of picture frame, top left).

line (this is not my engine, though is the same)

This breather is also paired with a coolant line (the looped line to the left of the image) It seemed clear that heat had caused it to become disconnected since the rubber nipple that is part of the rubber intake tube was split (and hot). I reconnected the breather to the rubber intake tube with hose tape and shrink tape which seemed to provide a decent, if not very good, seal. I then babied it as I continued, occasionally having a lesser feeling of poor running that could be avoided by feathering throttle. I still managed to get over 34 mpg on the trip.

After reaching my destination, I was able to connect my ScanGuage II, which I didn't have with me before. It displays nearly all any info from computer and I've now been able to monitor intake air temp. It starts at ambient temp. on a cold start, but increases seemlingly in parallel to engine temp. The engine never heats beyond 215F or so, but the intake temp has been indicated at 147F at med. speeds - which is the only time I've felt the engine run poorly since patching the PCV breather. At highways speeds, it settles around 125F. I've driven 500 miles since the patch job (one rushed long trip) and only had the high intake temp after stopping for a bathroom break - it quickly settled back down once I was back up to highway speed.

I've not had time to do much troubleshooting yet, but thought I would post here to solicit some advice on trouble shooting strategy.

In summary:
-no check engine light, engine temp fine
-sudden poor running and thump under load - stopped immediately
-pcv breather disconnected from intake tube, seemingly because of heat
-patched pcv breather back to intake tube
-reset computer by disconnecting battery (locked up my stereo too!!)
-replaced sparkplugs (prob unrelated, but worth noting)
-running well with good response and fuel economy 99% of the time
-hooked up scanguage and noticed elevated intake temp.
-only sign of poor running was when intake temp reach 147F at med. speed
-pcv valve seems fine, clean, rattles, works as one-way valve upon blow test
-no problem at all at high speed. 34+ mpg

My thoughts:
-pcv breather may be putting extra hot air into intake. my understanding is that most flow in this breather should be FROM the intake and not TO the intake
-could be excess blow-by, but other indications do not point to this (good response, good fuel economy, no smoking, etc.)

My strategy:
1. replace pcv valve even though it seems to be working fine
2. remove, inspect, and clean coolant line that runs parallel to PCV breather

Any thoughts and suggestions will be very much appreciated.

 

Compression test?
How about cleaning out the inside of the large rubber intake duct & throttle body. Then see how long does it take to get full of oil again. That might give a hint about how much or how often that breather flows backwards.

I've a feeling that you can get a fair amount of backflow (from engine to intake) and still run OK without misfiring etc. So either a compression test or checking the oiliness of the intake to see whether that's happening.

Got a hose clamp on that connection where the breather attaches to the big rubber intake duct? (I think I see a spring-type clamp on there but it's not your engine anyway...) How about mechanical movement pulling it apart? There really shouldn't be any pressure to speak of in that tube.

Replacing the PCV valve is pretty inexpensive, even though it seems to be OK.

 

One possibililty is that PCV valve was installed prior to discharge, then excess crankcase pressure may be cause of it's ejection. Suggest inspecting PCV air intake hose and PCV outlet hose for obstructions. Pinch PCV outlet (downstream of PCV) and see if a click is heard (PCV closing).

IAT appears downstream of PCV inlet, so large amounts of crankcase blowby would elevate IAT.

good luck

 

thanks for the input. I'm busy finishing up my master's thesis at the moment, so it'll be a few days before I start troubleshooting.

I actually haven't confirmed that oil is getting into the intake, so I'll check that first.
replacing PCV valve will be next step. Will give you all an update when I do. Thanks again!

 

New rubber lines or vac hoses and you should good to go.I clean out my pcv valve with brake kleen at every oil change and reuse them.They rarely every go bad.When the hose are broken,or split,you get vacuum leaks and that causes rough running,hunting or abnormal idles.

For fun,You can also do a few home made tests in addition to the info. everyone posted already. You can block off the systems and go for a test drive to note the changes if you want.

You can unplug the PCV hose and cap the vacuum inlet port at the Intake/TB side areas.They sell rubber vacuum caps in kits with different assorted sizes in any auto parts stores,to cap off any unplugged inlets.

I have done this to allow the engines to run without vacuum leaks.You can leave the pcv and hose plugged into the valve cover, but unplugged from the intake side,with intake capped off.That will stop any vacuum leaks.It might help you to see if the crank case is pushing the pcv out or not as well.

Its not suggested to drive the car very long this way,but enough for personal tests for data. The car is designed for the intake manifold to draw the pcv out of the engine as well.But then again,like older cars,you can put breather filters on the valve covers to replace the pcv valves itself.I have done this on Gm TunePort MPFI engines before with no trouble.Had a Engine pulled a steady 21 inches of vacuum with breather filters on the valve covers and no vac leaks anywhere. The PCV systemn was removed.

I think you are fine and maybe just check the hoses and lines for any broken connections and repair them.

 

Thanks for all the advice. I'm finishing up my ms thesis, so not much time to work on the car at the moment... I did replace the PCV valve though. When I checked the old one again I found that it was clogged. (I know I could just clean it, since a new on is just a few dollars...)

No change yet... Still getting hot intake air. The car runs around 210F all the time. the intake air levels off around town at about 145-155F (when it's 90F outside). At highway (70 mph) speed the intake air is lower, around 120F.

Will give another update when I can do more troubleshooting...

Thanks for all the help, folks!