ok having searched this illustrious website for a good hour or 2 i cant seem to find an answer to my problem..
Just wondering if anyone could clarify to me the most likely cause..

BACKGROUND:

bog standard bar a catback exhaust UKDM 2.2 vtec - H22a

The car is fine, no problems..

I'm cleaning the car and whatnot open the bonnet to find I have left the oil cap off the week before when topping up the oil (i know, i know.. i can see you shaking your heads now..) So it aint a pretty sight.

Top up oil, put the cap back on.

Out on business driving approx 150miles all on motorway (or "free"way for you yanks tho i dunno what's free about it ).

I get a cel after 30mins driving or so between 70-80mph.

I cant feel any effects of what's causing the cel so I pull over at a service station.

My idle is *****. its drops to like 100rpm, shakes the car to buggery, almost stalls but not quite then returns to normal (750-800rpm).
A tap on the accelerator (gas) pedal sees a healthy roar of my beast followed by the almost stalling scenario.

I turn the car off and back to the on position to see if i can get a cel reading. the lil git cel has disappeared. engine light on.. engine light goes back off.. wtF.. with a rather bemused look on my face coupled with relief that its gone I start the car to find the problem is still there.

I can drive the car ok.. it's just stopping at traffic lights or in that stop-start traffic that the idle is as described above "*****"

Now when i start the car from cold, the car is fine again.. idles at 750-800 after warmup and shows no signs of the ***** encountered earlier.

Low and behold after 20mins or so driving back down the motorway, on comes my mate the engine management light! i dip the clutch to test the idle and yup - dun dun dunnnn..... ***** is back!

i notice a bit of shaking by the car but im not sure if this is down to me being paranoid by this point.

I think phukkit and just drive home at the speed limit or below (seriously i had never done a whole journey doing these speeds before and sheesh it's boring).

When i got a chance (empty road etc) i dropped it down to 3rd to test out performance.. vtec still happily surges my car forward and my *** backwards so definetly not in limp mode or suffering any abnormal performance effects.

On my daily commute (10 miles each way) over the last week this ***** has only happened once.

Obviously it bothers me as I dont want it getting worse.

Now having searched I come across a couple of options.. (i think)

it's not the Fast Idle thingy cause thatd cause idle to be high.. right?

the EACV needs cleaning? i can understand how this would cause the low revs but why only when the cel comes on?

o2 sensor need replacing? again why would it only intermittently (while warm) do this? so Im doubting this is the cause either..

Without getting a CEL code as it disappears when i turn the engine off - i'm clutching at straws..

Not sure if the whole leaving the oil cap off has anything to do with the problem whatsoever, but seems coincidence i notice that and then get this ***** problem.

hmm..

another n00b with a problem signing off.

Any advice would be appreciated from the prelude-guru's of the world!
or anyone for that matter..

Gavz

PS i did clean up the oil smeared over my engine bay and intake manifold left by my oil cap blunder and had ***** since..

Random Irrelevant Fact: Honda UK are not only expensive.. (£300 (almost $600) for a downpipe + tax + gaskets + fitting) they are also useless monkeys with no specialist Honda mechanical knowhow. if i had some overalls and a spanner in me pocket, I could get a job as a workshop superviser!

 

When your car is cold it is in open loop and when it gets hot it is in closed loop and lots of things happen, the O2 sensor starts working later, not cold, those idle things you talked about change their state of operation. What ever is happening you need to tell us what the CEL code is , get it chacked and let us know for additional help mate.