Re: 2001 Focus 1.6 Zetec engine, 60K miles: MAF sensor

Sorry, forgot to mention this is the UK RHD model. 1.6 Ghia petrol, regularly serviced and in otherwise excellent order.
Morse

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Either you have a vacuum leak, or your throttle body is dirty, or indeed the MAF is giving varying signals.
The MAF is located just on top of the air box on the hose to the intake manifold. A quick check is to disconnect it and go for a drive. The MIL will be lit, but if the idle quality is better or the same (not worse) then the MAF is at fault.
Check for intake leaks very carefully first though.- espcially the PCV system.
I would also blank off the EGR valve for trial purposes too. Disconnecting the actuation will not stop a physically leaky valve leaking.
Tim..
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Tim, thanks for your reply.
I'm struggling a bit here, I can't find any electrical device attached to the hose-
http://i196.photobucket.com/albums/aa223/morse248RPA/engine.jpg
http://i196.photobucket.com/albums/aa223/morse248RPA/airboxhose.jpg
The only thing that I can see on the intake system which could be the MAF is located on the end of the bottom of the manifold before it branches out-
http://i196.photobucket.com/albums/aa223/morse248RPA/Intake.jpg

Is that the crankcase ventilation system, the small hose which goes to the airbox? It seems secure but I'll recheck.

I'm not 'absolutely' sure I know which bit is the EGR valve, my guess is this-
http://i196.photobucket.com/albums/aa223/morse248RPA/closeup.jpg
If I'm right, I need to remove the large pipe with the red/black connector and plug both the valve and pipe?
Your help is much appreciated Tim.
Morse
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You have a MAP equiped 1.6, rather than MAF- this system works on air pressure rather than volume. You will need to remove the MAP sensor, as the small air pipe often blocks with oily crud / deposits. Do NOT use carb cleaner / air line directly into the map sensor, if its little pipe is blocked, blow across the top of it with your cleaner.
There is no EGR on your car- the device you marked is the fuel pressure regulator.
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Tim.. wrote:

Thanks Tim. Do you know where the MAP is located by any chance?

Oops! There's so many hoses and odd looking gadgets on 21st century cars! A far cry from something like a MkI or MkII Escort that's for sure!
Morse
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You already pointed it out in one of the photo's-it's between number 1 and 2 intake runners.
Tim..
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Tim.. wrote:

Cheers Tim, looks like an alternator off job, can I disconnect it to run tests the same as the MAF sensor?
Morse
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You're looking for a PWM ~0.5 to 5v output on pin 2. I tend to use the tacho function on my DVM if I havent my scope handy.
Tim..
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Thanks Tim, I'll have a look at it.
Morse
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Tim, I haven't got around to checking the signal from the MAP sensor, but it seems the fault has taken a new twist. While I was driving it yesterday it appeared to be picking up speed by itself and when I depressed the clutch and took my foot off the accelerator the revs sat at 3000 rpm! It did this intermittently- sometimes the idle was fine, sometimes it was at around 1000-1200 etc. I managed to drive a good mile without touching the accelerator at all! The prime candidate for this fault seems to be the IACV, but I've just changed that. It doesn't rule out the new one being a dud of course. I'm more inclined to think the IACV is being wrongly controlled due to the ECU getting duff info from somewhere (TPS, perhaps? I'll recheck it).
My (layman's) theory is the TPS is dodgy and is telling the ECU that the throttle is open more than it is, causing the ECU to inject more fuel and therefore richen the mixture, initially causing lumpy idle. The ECU detects the rich mixture and opens the IACV to allow more air to attempt to weaken the mixture, causing the high idle. Does this sound feasable to you, Tim?
When I parked up I thought I'd gradually depress the accelerator and see what happened. The revs didn't pick up smoothly and when it got to around 2500 (IIRC), it hit a spot where it was speeding up/slowing down rhythmically. Increasing the throttle past that point actually caused the revs to dip quite a bit, it seemed to struggle then pick up again.
On the road, I've noticed that it now runs out of steam at around 4500 rpm. IOW, it's not keen to rev anymore, though it performs well up to this point. Cruising on the motorway at 70mph it seems perfectly normal, no misfiring or anything like that.
I'm at a loss, do you have any suggestions based on the above info? I'd bung it in the garage but money is really tight right now and since I used to do all my maintenance myself, I'm able to change most easily accessible components. I really appreciate any help you can give.
Morse
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TPS is the usual cause of a stuck high idle, check its output..
tim..
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Tim.. wrote:

Tim, I spent a while with it this afternoon. The voltage from the TPS is 0.955 at idle, close to 5V at full throttle. When the revs get to around 2200 rpm, it fails to increase with more throttle, but the voltage from the TPS increases as one would expect. Keep increasing the throttle and it reaches a point where the revs suddenly pick up and hit 3000, then all seems normal.
I also noticed if you snap the throttle open quickly while idling it hesitates before it picks up. The hesitation makes a slight 'cough' and there's a very brief dieseling sound before it picks up.
I'm still stumped! I couldn't get it to stick at high revs like it did the other day so I couldn't take any measurements. I might rig up a semi-permanent voltmeter in the car so I can monitor it on the road. A faff on but it might give me some insight as to what's happening.
Morse
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