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jkoebel
 
2003 Ford Focus ZX5 (16 valve engine) "stumbles" a bit at idle.

My friend just bought a car for $5800 from a used car lot. 03 Focus with 80k miles, not too bad. I don't know that much about automotive mechanics but I do tinker on my W123 Mercedes so I went along to vet the car out a bit.

It looked like either the dealer had done a great job hiding any problems, or there weren't any major ones. No leaks, correct fluid levels and good color, belts in good shape, etc. But we took it out on a test drive and it would "stumble" at idle a bit.

We tried it with the A/C off and with it on and it made no difference. It would idle okay for a minute, then the idle would drop really low like it was thinking about stalling the car would shake a little bit, then the idle would pick back up.

He bought it, and drove it home, and on the ride home it "revved like it was in neutral" once on the highway when he "floored it" (automatic transmission). I think that he observed it kicking down into a lower gear for acceleration, but I want you guys opinions on that.

I tentatively diagnosed the problem as either a bad O2 or MAF sensor. I had a '98 Honda which had the O2 sensor go bad after about the same number of miles, and the symptoms were shaking, stumbling idle that would occasionally be okay and occasionally drop very low.

What do you guys think?

It's a regional dealer in Melbourne, they've been written up in the papers in that area a few times as being a very reputable place, and had a TON of business while we were there -- steady stream of people in and out for test drives, buying, etc. And they have a shop in the back to do the repairs and stuff.
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Old 06-12-2008, 07:11 PM jkoebel is offline  
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Bluesultan
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engine size? you say you're in Melbourne so i'm not sure it that's still the same 2.0 Zetec. also, are you getting a check engine light? if not, it's probably not a bad O2 sensor or MAF sensor...bad sensors trip the check engine light.
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Old 06-12-2008, 07:40 PM Bluesultan is offline  
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prometheum
 
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you can try cleaning the MAF with some non-chlorinated brake parts cleaner first, reset the ecu and try again. also dirty idle air controller?
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Old 06-12-2008, 07:41 PM prometheum is offline  
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Bluesultan
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Originally Posted by prometheum View Post
also dirty idle air controller?

this or maybe you have a bad DPFE sensor. again, is the check engine light on?

edit: check out this thread

http://www.focushacks.com/index.php?modid=80
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Old 06-12-2008, 07:45 PM Bluesultan is offline  
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jkoebel
 
Melbourne, FL -- not Aussy, should've been more clear. Sorry.

I didn't have a CEL when my sensor died, unless sensors have gotten better I think it could still fail even though there is no code. I think there are other modes of failure than "fail-open" (which I'd expect to throw a code), like "fail-report-the-wrong-value-randomly" sort of thing.

Thanks for that thread on Focushacks, that seems a good place to start.
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Old 06-12-2008, 07:59 PM jkoebel is offline  
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jarhed13
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"revved like it was in neutral"

That would be it downshifting, and still not having enough torque to feel a kick....
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Old 06-12-2008, 08:01 PM jarhed13 is offline  
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Ed355
 
While an IAC may cause this, its most likely a vacuum leak. Check your pcv hose, its probably collapsed. It's at the back of the engine on the intake, comes around to the left of the engine (where the thermostat housing is) and connects to a hard line there. after the hard line it goes back to a rubber hose to the pcv valve (under the exhaust manifold). This is on the Zetec engine, which I believe those cars still had in 03.
Old 06-12-2008, 08:02 PM Ed355 is offline  
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jkoebel
 
The car nicely has a vacuum diagram on the inside of the hood so I'll also check that. Cool.
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Old 06-12-2008, 08:08 PM jkoebel is offline  
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Rancidpunk666
 
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First step, clean the MAF sensor and the throttle body.

Second step, check for vacuum leaks by introducing propane gas near all vacuum lines.

3rd step, Check the IAC counts

4th step DPFE replacement

5th step Take it back to the dealer and tell them that they sold you a car with problems.
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Old 06-12-2008, 09:14 PM Rancidpunk666 is offline  
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gribly
 
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Quote:
Originally Posted by jarhed13 View Post
"revved like it was in neutral"

That would be it downshifting, and still not having enough torque to feel a kick....

My escort's automatic has done this it's entire life. If I floor it at about 55mph it will free-rev, and snap into gear when it winds back down. Doesn't bother me enough to replace the tranny with a junkyard one.
Old 06-14-2008, 02:13 PM gribly is offline  
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flshdncr
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Stumbling and shaking at idle...let me guess, it also drops rpms? Poor acceleration? You have a cylinder that isn't firing.

it's rev'ing because it doesn't have enough power to accel, so it downshifts and still doesn't have enough.

Pull plugs to see if one is obvously discolored. If that doesn't tell you anything, then try getting the car to idle poorly and then disable one spark plug at a time. On my 3000GT I can do that thru a datalogger, I'm sure OBDII lets you do something similar.
Old 06-15-2008, 09:27 AM flshdncr is offline  
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prometheum
 
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Quote:
Originally Posted by brkdncr View Post
Stumbling and shaking at idle...let me guess, it also drops rpms? Poor acceleration? You have a cylinder that isn't firing.

it's rev'ing because it doesn't have enough power to accel, so it downshifts and still doesn't have enough.

Pull plugs to see if one is obvously discolored. If that doesn't tell you anything, then try getting the car to idle poorly and then disable one spark plug at a time. On my 3000GT I can do that thru a datalogger, I'm sure OBDII lets you do something similar.

if it was misfiring it should have a code or a flashing check engine light
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Old 06-15-2008, 09:30 AM prometheum is offline  
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jkoebel
 
Quote:
Originally Posted by brkdncr View Post
Stumbling and shaking at idle...let me guess, it also drops rpms? Poor acceleration? You have a cylinder that isn't firing.

it's rev'ing because it doesn't have enough power to accel, so it downshifts and still doesn't have enough.

Pull plugs to see if one is obvously discolored. If that doesn't tell you anything, then try getting the car to idle poorly and then disable one spark plug at a time. On my 3000GT I can do that thru a datalogger, I'm sure OBDII lets you do something similar.

Yeah, RPMs drop ad idle also. Acceleration seemed okay, but that's coming from someone who drives a 3900 lb. vehicle with a 63 horsepower engine, so it might in fact be slow as a dog and it feels like a lightning bolt.

I didn't get to checking it yesterday for several reasons, will try again soon.
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Old 06-15-2008, 10:02 AM jkoebel is offline  
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