petrol focus unsteady idle

sorry, it is a 1.8 not 1.6

It's a bad day if you're asking, Mr C.

The only one I've ever looked at I asked about here. Turned out to be an injector in the end.

I was asking more for fun than anything !! and no one knows all the faults, after all someone might know it was the epicyclic dimodulator unit or something !

I have 99 per cent identified the culprit as the MAF sensor. With it connected the idle is hunting and it can stall, with it disconnected the idle is rock steady . Reconnect it and it may stop or go back to a rough idle.

My money would be on the PCV box under the exhaust manifold.

Tim..

Well, I found it in the end, it was actually a tiny air leak that probably increased when actually decelerating (extra vacuum) on the bend in the pipe from air box to inlet manifold right at the manifold end. I initially sprayed around the area and got no changes, but after actually feeling around everything I started to be able to hear the leak and after that it was easy. Interesting how disconnecting the MAF sensor made it run really well !! That foxed me for a while.

In message , Mrcheerful writes

Taxiing out at Chicago the Captain announced that "We have a light on the panel, so we're going back to the gate". I listened to three engine run-ups and shut-downs and hoped that it was the light on the panel which was faulty. ;-)

I suppose it must have been...

Nedavno Mrcheerful napisa:

What did you sprayed with?

Idle control valve :) .. I'm sooo ameteur it hurts lol. But I had a over revving problem once and thats what it was. Actually same problem twice secdon time was the MAF, log some live data and compare I guess.

Bet the answer has been found already, must read threads before posting hehe

I normally use wd40

carb cleaner till I ran out and then contact cleaner, which actually seemed better for the job.

Nedavno Mrcheerful napisa:

And how noticeable is the rev change to the untrained ear?

it was more of a unevenness. when I put a digital counter on, the revs were only changing by less than 100 rpm total. The difference when the maf sensor was disconnected was quite sharp and the idle steadied to just a handful of rpm change. Apparently the reference that the ecu assumes with the MAF disconnected is a bit on the rich side, so the idle smoothes out.

Nedavno Mrcheerful napisa:

:-) I could spray all day long, and detect nothing.

Mrcheerful expressed precisely :

I would go with either vacuum leak or idle valve sticky.

if there is a leak and you hit it with the spray then you will notice the change in tempo.

Common sense really - unplugging the MAF makes the ECU calculate air flow based on throttle position and engine speed, so assuming no air leaks POST throttle it will run almost lovely. The MAF reading was lower than it should be cos of the leak in the trunking.

Tim..

The leak was not in the trunking, that would have been easy to find!! The leak was post throttle, the leak was in the half inch breather pipe that runs from the inlet manifold quite low down, comes around the end of the engine and attaches to a metal pipe, I didn't actually check, but I imagine it is the one that goes to the engine breather box on the front.