Won't idle when warm

Won't idle when warm

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newuserhere

Original Poster:

40 posts

102 months

Thursday 17th November 2016
quotequote all
Car: mk2 (54) focus; 1.6l petrol

Problem:
When cold rough on idle
When warm cuts out when falls to idle
When warm sometimes won't start without foot on throttle. If it does start it will hit about 900rpm then fall until cuts out
I can hold foot lightly on pedal and although a tad rough holds fine. If I rev up it runs smoothly and nicely! Can rev to red line spot on.

I've looked at live data and voltages seem to change for pedal position and throttle butterfly position between pressed and not pressed. Although whether they are reading correctly or not I don't know.

I bought it with timing slip. Put 8 new exh valves in and the works. Although that's a common problem on these it seems.
I don't think it's related though as it wouldn't run smoothly when revving if there was engine problems.

Any ideas?

Edited by newuserhere on Thursday 17th November 16:47

colin_p

4,503 posts

219 months

Thursday 17th November 2016
quotequote all
The MK1 1.6's had an old fashioned idle control valve. I think yours is a MK1.5 being a 2004 so would assume the engine is the same.

With those ICV's sometimes you can get away with cleaning them with carb cleaner, other times you'll need to replace. Worth cleaning as a starting point.

They also have a vacuum hose(s) that runs between the inlet manifold and head which can split and cause idle problems as does any vac leak. How were these hoses when you did the build?

newuserhere

Original Poster:

40 posts

102 months

Thursday 17th November 2016
quotequote all
It's a different engine with electronic throttle body. Tried cleaning that no difference

newuserhere

Original Poster:

40 posts

102 months

Thursday 17th November 2016
quotequote all
Also had breather pipe off no splits

Rat_Fink_67

2,464 posts

213 months

Friday 18th November 2016
quotequote all
Lumpy/misfire at idle, but then revving up cleanly can often be the early stage of coil pack failure on a Zetec. Being worse when warm is another symptom too. The wiring harness and connector can often deteriorate as well so worth checking. These engines tend to be quite sensitive to ignition issues, have you checked the spark plugs (the porcelain cracks quite commonly) and resistance of the leads?

newuserhere

Original Poster:

40 posts

102 months

Friday 18th November 2016
quotequote all
Plugs have been changed. Checked gaps today also.

I have a mk1 1.6 focus so switched all Ht leads and coil pack across and no different.

Gonna see about the throttle body next.

Map pressure seems to spike with revs dropping

S0 What

3,358 posts

179 months

Friday 18th November 2016
quotequote all
Is it a zetec or zetec SE? if the SE check the breather pipe from the thottle body to the rocker cover, they go soft and can split or collapse inder the inlet runner pipes, if the zetec check the breather from the crank, has the belt been done recently? had similar issues when they've been done using the tippex method and not the locking pin/plate method with the cam pullys slackened and retighted after the belt is tensioned ?

newuserhere

Original Poster:

40 posts

102 months

Friday 18th November 2016
quotequote all
The rocker Breather entered inlet before butterfly valve

S0 What

3,358 posts

179 months

Sunday 20th November 2016
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newuserhere said:
The rocker Breather entered inlet before butterfly valve
Doesn't matter it still causes idle issues, i repair them a fair bit, ford want 30 odd quid for new ones and my tight arse customers prefer i insert some hard platic tube to replace the split part.
Not saying it is your issue but it can be.

newuserhere

Original Poster:

40 posts

102 months

Sunday 20th November 2016
quotequote all
Nah that's not my issue. Even if split it's just drawing in unfiltered air in the same way as it does from filter. Map pressure is still controlled by the ecu/throttle body