MK1 Focus - Erratic Idle

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#1
The Re-created thread!

I will try to remember all that was discussed.

The Car:
2002 Focus ZX3
2.0L Zetec DOHC 16v
MTX75 Manual Transmission
199,500 miles on car

The Problem:
A few weeks ago, my car started to develop a warm-engine stall. After some google searching I decided the most likely cause was the Idle Air Control Valve (IAC) going bad. I replaced it with a new unit from a local auto-parts store.

With the new IAC installed, I started the car and it immediately rev'd to 3000 RPM (something it has never done before) and eventually settled down to 750 rpm (normal idle).

While driving, the car now will maintain or climb in revs between gears (up shifts and down shifts).

If I clutch-in coast, the car will hold revs and climb by about 250 rpm, but won't settle out (drop to idle rpm) unless the speed reported on my speedometer reads close to 10mph or less.

If I clutch-out neutral coast at speed (only tried this at 55-65 mph), the car will first start to climb in revs, then will start to fall down to around 1500 rpm, then jump back up to 3500 rpm. It will continue to oscillate like this until I put the car into a gear.

If I turn the A/C on while the car is at 750 rpm stationary idle, the rpm will drop to 600 rpm then shoot up to 1250, and start to oscillate between those two numbers. I now have to drive without my A/C on.

What I have tried for fixes
One of the first things I tried was resetting the ECU. I had read online where sometimes replacing smog or engine control components causes the PCM to not control the engine as it should and a reset is needed so that the PCM can learn the new part. This helped a little, but did not fix the problem.

I tried cleaning the MAF sensor with MAF cleaner spray. This did not make any noticeable difference.

I tired unplugging the MAF while the engine was running at stationary idle (750 rpm), the engine stumbled noticeably and recovered to a stable idle. I did this several times with the same result. I think we can rule out a faulty MAF sensor.

What I'm planning to do
When I have time this weekend I'm going to pull the IAC and check the gasket for damage.

I am also planning to replace the following components:
Spark Plugs
Spark Plug wires
Throttle Position Sensor
Valve cover to air-box breather hose
PCV Valve
PCV Valve hoses

----------------------------------------------------------------------------------------------------------------

Ok, I think I pretty well summarized everything that had previously been discussed before the database error that ate the last thread.

If I missed something, please re-post.

If you have an idea of something for me to try, I'd be interested in hearing!
 
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Thread Starter #2
I forgot to add to my initial post that it has been suggested by a couple members that I check for vacuum leaks.

I have not ruled vacuum leaks out as a possibility. However, due to how many vacuum hoses there are and how time consuming the check might be, I'm saving this test as a "last resort".
 
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#3
I also added that if you disable your MAF you should be able to feel the engine idling rough. If you disconnect it and there is no change in idle then you might have a bad MAF.
 
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Thread Starter #4
I also added that if you disable your MAF you should be able to feel the engine idling rough. If you disconnect it and there is no change in idle then you might have a bad MAF.
That's right you did suggest that, and on that topic, I tried unplugging the MAF sensor last night with the engine running at a stable 750 rpm idle.

As soon as I got the connector un-plugged, the engine noticeably stumbled, almost to the point of dying, but then recovered to a stable idle and didn't idle any significantly different than with the MAF plugged in.

I plugged the MAF connector back in and waited a couple minutes and un-plugged it again. It did the same thing, noticeably stumbled almost died but recovered to a stable idle.

Based on this, it seems to me we could reasonably rule out a bad MAF for the time being. Correct me if I'm wrong on my logic here.
 
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Thread Starter #7
Ok, going to be a bit of a longer post so bare with me.

Worked on the car today, I replaced spark plugs, spark plug wires, valve cover breather hose and PCV valve. The spark plugs themselves looked good, nice tan color. I checked the gaps on them as I pulled them out.

Factory gap is 1.3mm
Cylinder Gap
1 1.35mm
2 2.2mm
3 1.35mm
4 2.3mm

So they were due for replacement, I checked all the gaps of the new plugs as I put them in. Motorcraft brand and they came pre-gapped right at 1.3mm

I also cleaned the throttle body with some throttle body cleaner.

Now, for the IAC.

I pulled the IAC and checked the gasket. Gasket looks fine, no damage. I feel around on the intake manifold where the IAC bolts up and I feel a couple o-rings, apparently the Factory IAC doesn't use a gasket, it uses o-rings to seal to the intake manifold. So I pull the o-rings out.

Now, I kept the original IAC valve that I pulled, just in case and for comparison purposes. I bench tested both by connecting them to a 12v car battery. The IAC on this car is a simple two-wire solenoid and plunger style IAC.

With the factory IAC connected to a car battery you can hear the solenoid click and see the plunger move.

The "New" IAC I took off the car, you could hear the solenoid click but I the plunger did not move. So maybe this IAC is bad.

I took the new IAC back to the parts store and exchanged it (It came with a 1 year warranty). Got home and immediately bench tested this replacement IAC. Again, car battery, solenoid clicks but plunger doesn't move.

Well, I went ahead and put the new IAC in just to see if the car ran any different. I had disconnected the battery when I started working so the ECU reset. I started teh car, it immediately went up to 3250 rpm, then settled down to 1000 rpm idle. As I waited the next 15 minutes with the car running, it settled down even further to a nice warm engine 750 rpm idle.

I went for a test drive. The car behaved much better. It would momentarily hold rpm between gears, but drop down as I held the clutch in and selected the next gear. Neutral coasting was better too, with the vehicle in neutral clutch out, it would drop down to around 1500 rpm while the vehicle was moving. Big improvement.

I got back to the shop where I had been working on the car. shut it down and let it rest for about an hour. Came back and did a warm-engine start and it did well. Started at 2000 rpm and quickly went down to 750 idle.

As I start to drive home though, things start to go bad.

Now when I go to change gears the RPM Shoots up to 4000 rpm between gears AND, when coming to a stop (where normally it would at least settle down to idle) it will now try to go back to 4000 rpm out of gear not moving.

This is getting very frustrating and just doesn't make any sense.
 
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Thread Starter #8
Ok! So...

After some additional snooping online/youtube I found this video:

https://www.youtube.com/watch?v=gLXmr2TVUtg

This guy talks about replacing everything I did (PCV valve, Throttle Position Sensor, IAC) and he still has a high idle problem like me. He ended up replacing the rear PCV hose that plugs into the back of the intake manifold. The reason being is that apparently when that hose gets old, it starts to collapse under vacuum.

Here is a really good video of the hose collapsing when the engine is running:

https://www.youtube.com/watch?v=qR0f_yfBPTQ
(skip to about 2:20)

The annoying thing about this is that I actually bought a brand new PCV valve hose kit that includes that hose but ran out of time to install it today.

So I will be back at the shop tomorrow to replace that hose.

I will update all of you tomorrow!
 
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Thread Starter #9
Another day of working on the car and another update, this time positive!

I replaced the PCV hose that was collapsing (20 minute job) and reset the ECU again. Since the car had 30 miles on the ECU since the last reset with a bad PCV hose, I wanted to give it a clean slate to start with.

Initial start-up went much better this time. Instead of rev'ing out to 3000 rpm and holding at cold start, it rev'd briefly to 2500 then quickly started to drop down to a nice 1000 rpm cold engine idle.

Test drive also went well, the engine rev's only with throttle input. It holds rpm between gears only briefly, if you are lazy/slow with your gear changes you can see the tach needle start to drop after 3-4 seconds of clutch-in.

With the engine warm, stationary idle (car not moving) is 700-750 rpm. If the car is in motion, the rev's will only drop to 1500 at the lowest, until the vehicle speed is 15 mph or less, which is fine.

I still have 1 problem though, and it has to do with the Air Conditioning affecting engine behavior.

I noticed on my test drive that if I turn on the A/C, the engine still wants to rev out to 3000 rpm on it's own.

If I bring the car to a stop (A/C still on) the engine will hold that 3000 rpm for about 15-20 seconds, then rpm will drop so quickly it stalls the engine. Warm-engine restart is fine though (A/C off).

So my plan now is to drive the car for a week without using the A/C (which will suck this week in california in the 99-100 degree weather we are going to have this week). This is to let the PCM/ECU do some learning.

Next week I plan to start trying to use the A/C again.

However, if anyone has any ideas of another problem I might be having related to the A/C that would make the engine behave like this, I'm interested.
 
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Thread Starter #11
Alright!

Good News everyone, my car is fully fixed now!

So last time I posted, I mentioned that the erratic idle was mostly solved by replacing the PCV hose that was collapsing, but I still had some in-consistent idle/engine rpm behavior with the replacement IAC.

To summarize, after replacing the PCV hose and with the new IAC, the car would run basically fine, but it wasn't behaving like it used to IE dropping revs between gears upon clutch in, rev hangs, Cold start rpm higher than usual. I also couldn't use my Air Conditioning as doing so would cause the engine to rev out to 3000 rpm on it's own in neutral, and then at stops the rpm would drop so fast it would stall the engine.

So I decided to once again replace the IAC, but this time I bought a Delphi unit from Amazon instead of getting another Oreilly Auto Parts unit.

And now my car behaves like it should. The revs drop off once the clutch is disengaged, AND I can use my air conditioning again without it making the engine rev-out.

While I had the Oreilly IAC out of the car and before I installed the Delphi, I took a moment to take some pictures of all 3 IAC valves (I still have the factory one). There are some differences between the units and I can't help but think those might be critical in proper behavior.

I'm going to do a separate write-up thread for the IAC valve comparison, I think you will all find it interesting, and hopefully there will be some useful information for the next person looking to replace their IAC valve.

Cheers everyone! [raceflag]

Oh, and last night my car turned 200,000 miles!
 
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Thread Starter #12
Just a quick follow-up, for visual comparison I took a couple pictures of the old (bad) PCV hose and the new updated replacement.

*DISCLAIMER - I took these pictures with my cell phone as it was all I had at the time, quality isn't great but it's good enough!


So the old hose is the black one, the new hose has the silver foil heat shield around it.

This next picture shows how, just with my fingers I can collapse the hose.


If I pinch the new hose in the same place, I cannot collapse it with my fingers.
 
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#13
I would also adjust your idle , start engine , disconnect the IACV , engine should die , restart and set idle about 650 , If the idle isnt set properly it will work against the IACV

The reason your idle doesnt fall below X rpm till you get to X mph is thats the way the idle/dashpot is set in the Ford tune

Tom
 
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#15
If your TB is stock then your going to have to bend the tab on the TB that hits the screw that sets the idle rpm , Ford seals this so you cant turn the screw

If you have a aftermarket TB then use the idle adjust screw but the IACV must be unhooked to properly set the idle either TB

Tom
 

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