Focus wont idle at traffic lights

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Car surges a little when driving

When at light it doesnt want to idle. Almost stalls. I adjusted the idle to 800 rpmin gear, 900 rpm in park,to keep it running. When i notch the idle screw up, just a bit, the engine races at close to 4000 rpm. So setting it is tricky. Do i have a leak somewhere?? Help!
codes? EGR dirty or faulty? IAC dirty or faulty? TPS bad? Vac leak? ICM going out? So many options.

Sure hope there are some codes to help here.
codes? EGR dirty or faulty? IAC dirty or faulty? TPS bad? Vac leak? ICM going out? So many options.

Sure hope there are some codes to help here.
At one point there was a code about iac. I changed it and the cel was off. But car still idles a little rough at traffic lights


Wrench. I help when I can
PLZ include vin # of engine. There are three 2.0l's available on this model car. The 8th # in your VIN is your engine. DO you have a 3, a 5 or a P?

Also, there are three different IAC valves available. Which one do you have, (not that it really matters) and how did you adjust idle?

These engines are NOT adjustable and if you screwed with the set stop screw which is factory adjusted and NOT meant to be fckd with, no wonder you got it screwed up and getting 4000rpm.

There is no idle up screw.
When i notch the idle screw up
Read the description in the ace 0 pdf I provided here.

Many things may cause a stall or stumble at idle, one of which is the most often a cause is a dirty MAF sensor which CAN be cleaned.

But first, you must find a way to set that throttle body back to factory if you can, cuz as of now, the PCM has no clue where the true idle is and will always have a rough or sketchy idle now that you have screwed with it. And yes, the pun is intended.

So tell us where on the throttle body you thought might have been a good idea to set idle up. I am assuming it is located on the throttle plate on the outside where the throttle stopper hits the set stop screw. Yes? If so, that was a big NO NO. Set it back 700rpm or so. That is where these engines like to idle when warm.

See my artistic skills in the snapshot. Screenshot (120).png



Wrench. I help when I can
There are two pre set stop screws I think on these which should never be touched. One is for the idle return set stop, the other is for the engine to know when it is at WOT.

When the set stop screw if meddled with, you just sent the TPS out of whack, hence the PCM is now confused with its preset algorythm and can no longer calculate proper load as the MAF will give conflicting readings in regard to the TPS reading and will try to ask the IAC to correct. See how this can confuse the PCM? Also, never disregard the PCV system, it is part of the the system and if that valve is clogged or the hose is bent, or leaking it will send your idle haywire.

SO, again, I will repeat myself, set it back to stock if you can, 700ish rpm and then we will diagnose the engine stall/stumble/surging from there. At this point it is useless trying to diagnose the idle issues since you have modified a preset factory adjustment which is not meant to be adjusted. There are or should be stickers in the engine bay that says just this, and all the manuals state that it is not adjustable.
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Wrench. I help when I can
And by the way, if I sounded cocky, I am sorry, but day in and day out I have to work on engines that ppl/clients fuss with when they shouldn't, and then they get pissed off at me when I tell them to stop screwing with imaginary adjustments. This is not a carburetor I say. It is a fully automated system. If something is wrong now, even after they spent hundreds of dollars on parts and still cannot get it right, I just say it is your fault, you caused a fully functioning preset system to go haywire.