NA Honda K20 not idling right


Started the car for the first time in a little while and it began to warm up at revs 1000-1200rpm, but after about 5mins went to 2000rpm and a couple of minutes later started to bounce between 1000-2000rpm every couple of seconds quite rhythmically. It drives ok but as soon as you go back to idle it does it.

Any ideas?

Cheers, Ian :eh:

I had similar once and it was a vacuum leak - perished hose check all those first.

Yup, hose or manifold leak can also be the IACV is getting stuck - unfortunately it still exists even on the Honda - easier to access though as its part of the throttle body.

Yeah I’ve had both a cracked manifold and a perished hose. When it did that hunting idle thing JDS fixed it I’ll have to look through my old emails…

Cheers chaps.

Sounds like it needs a visit somewhere. :frowning:

Any concerns driving it?

Nah I drove mine back from Bedford and then to Dudley. I did feel like a twat driving through London as every time I stopped it was rev’ing between 1k-3k revs like a reet boy racer!

Used to have same issue with mine after sitting over winter

Would try cleaning IACV

Is simple enough


You give me hope


yeah take the TB off, and then clean the IACV mounted on the bottom out with carb cleaner or solvent etc (petrol if need be).

Hi, been Googling the IACV cleaning and there’s a suggestion that before I do this I can test if it’s the problem by putting my finger over a hole in the throttle body. That sounds like a useful time saving test. But where’s the hole (that’s not Googling so well) and any tricks of what not to touch when the engine is running (eg. I and the butterfly will be moving with the surging)?

Cheers, Ian

Hole is where the butterfly meets the body at the bottom. Actual butterfly will be held shut by spring, revs are rising due to air getting into manifold another route

OK, thanks.

Let me try and make this more useful for others that may follow…

Here’s the throttle body, at the right-hand end of the fat red pipe…

And here’s the hole to cover (slightly blurred) at the bottom of the gold circle butterfly valve…

So then, I cover the hole and the revs settle. Have I found my culprit (definately/most likely/perhaps/etc)?

Yes. Pull the throttle body and clean the iacv. You’ll find that if the iacv has not been separated bofore then the 4 screws are a 5 spline torx just take them out and replace with an Allen cap head or the equivalent.

Use a light lube oil after a solvent cleaner. If you feel anything even slightly sticking or resistance it won’t work properly.

:slight_smile: Thanks

I did read that (with the K-pro ECU, that I have) some have removed the IACV with a blanking plate without impact.

Any thoughts on that? What’s the risk?

They usually clean up okay. A secondhand throttle body complete with all sensors are only £50-75 pounds. Not worth messing about with really.

can safely say bollocks to that, unless you want to be heel and toeing at junctions to stop it stalling when cold

OK then, it can stay.

Any tips for removing the TB? There’s lots of stuff going on back there.

Cheers, Ian

Ok so there are 4 connectors you’ll want to wiggle out: MAP and Purge valve atop, easy enough. TPS down the side by the bulkhead, no great shakes. The IACV is a pig in our cars as it’s rubber booted, under the TB and pointing towards the bulkhead. Then 4 bolts and off she comes.

I would order up a new TB gasket from Honda though, as they are known to pull apart when you crack the TB off where it’s lived for probably 10 years.

Will be the IACV I bet… had this happen to me once also… easy fix…