Slight miss at idle (only) - 99 Villager

[JWH46]

Howdy,

I gave my Villager a tuneup (60Kmiles) with new plugs and wires, and I still have this slight stumble at idle. Runs great at all speeds, but just at idle there is a slight miss. Any ideas what to check next?

[Airjer_]

Is the check engine light on?

[JWH46]

No, no check engine light. Runs like a champ otherwise. All maintenance done according to schedule. I ran a tank of Lucas fuel injector cleaner through it (at double strength) so the injectors should be kind of clean. It's not a horrible miss, but enough to annoy me. I might take it to my local independent mechanic, and have him throw a code reader on it.

[Airjer_]

If the check engine light is not on then there likely is no codes so scanning may not reveal any problems. This would also lead me to believe it is more of a mechanical failure rather than a "computer" or "component" failure.

These are notorious for bad fuel injectors but again if it failed it would have flagged a missfire code and turned on the check engine light. It may be possible that this is the start of something bigger and it may have to wait until it gets bigger to solve.

Unless the guy looking at it has some personal experience with this symptom in the past, it is likely you will have to live with it until it gets bad enough to start surrendering some clues to its origin!

It does seem like these tend to run ruff anyways so it may be a characteristic of the vehicle?

[JWH46]

I think you may have a point. I'm kind of a fanatic about my cars, and their maintenance, but I'd hate to pay for the mechanic to tell me they can't find anything.

[JWH46]

Well, swung by Autozone today, and had the codes read. It came up with PO325 - Knock Sensor. I thought I've read somewhere that something else (O2 sensors?) may cause this code to show up. No other codes were indicated, and the check engine light isn't on.

Any advice would be appreciated (before I take it to my mechanic).

[tempfixit]

The knock sensors rarely fail on these vehicles, something else is setting the code. Wish I knew the answer for you, you state that you changed plugs and wires. What about the cap and rotor??? Make sure the distributor does not play on the distributor shaft.

Here is another forum site that has a wealth of info and good people that could possibly answer your question:

[email protected]

[JWH46]

Well, I slapped a new distributor cap and rotor on it...and no change. It's gotta be a fuel injector or something else beyond my shadetree skills. I'll report back what my mechanic finds.

[JWH46]

Mechanic tried a new distributor, and that didn't make a difference. His meters showed it running really rich at idle, so it's new injector time. I'm going to have to save up for this one. Wow. Cheapest injectors I see are $115, times 6 plus labor is big bucks.

[Airjer_]

JW I'm not doubting your "mechanic" but I think I would get a second opinion before replacing all six injectors. Injector failures do occur on these but typically the injector will go dead and cause an obvious misfire, severe loss of power, and a check engine light.

There are many possibilities that can cause the O2's to go rich. Bad O2, Dirty MAF, pressure regulator, low compression, week spark, vacuum leak and EGR valve are some other possibilities. Just hate to see that kind of money spent with no results to show for it.

[JWH46]

I know, I thought about that, but his point was that you might as well do them all, rather than have to tear it down again when another one goes bad. It's running a ton better simply with the NGK plugs in there instead of the Motorcrafts, and with a fuel injector cleaning. I'm going to wait off on the injectors since it's running so much better. I think the only other thing I should do is clean the MAF, but I bet it isn't very dirty, with only 58K miles on it.

Thanks for the tips.

[Airjer_]

You would be surprised what can sneak past an air filter! There is a screen in front of the MAF that catches the bigger stuff. We get them quite often in late spring almost completely covered in cottonwood!

[Dennis Steele]

We are having nearly the same problems on the same vehicle.
I tuned it up....plugs, wires, cap, rotor etc.

Misses at idle and sometimes dies.
We took it to a mechanic and they replace the mass air flow sensor, o2 and something else.

It ran ok but with a slight miss. After 2 days it was back to stalling at idle.

A freind scoped it and told me it was the knock sensor.

Well I picked one up but I can't figure out where to put it!
After reading the advice here I am not so sure that this will solve it but I might as well put it in since I have it.

Where does it go?


PS.
Hi Airjer! :-)

[JWH46]

Originally Posted by Dennis Steele

We are having nearly the same problems on the same vehicle.
I tuned it up....plugs, wires, cap, rotor etc.

Misses at idle and sometimes dies.
We took it to a mechanic and they replace the mass air flow sensor, o2 and something else.

It ran ok but with a slight miss. After 2 days it was back to stalling at idle.

A freind scoped it and told me it was the knock sensor.

Well I picked one up but I can't figure out where to put it!
After reading the advice here I am not so sure that this will solve it but I might as well put it in since I have it.

Where does it go?


PS.
Hi Airjer! :-)

Dude, take it back... I've heard it's very common on these engines to get the knock sensor code. All that means is the knock sensor was activated by something else, so that's probably not it. Have the codes run on your van, and see if anything else shows up.

On mine, there were no other codes, so just as you did, I gave it a full tuneup. I just cleaned the MAF yesterday, and that didn't fix it either. My good local mechanic spent half a day working on it, and showed me on his fancy meters how the fuel pressure gets funky at idle and it runs rich. Then, when driving, all is fine. So, for me it definitely is the fuel injectors. However, with everything I've done, it runs so well, the stumble at idle isn't really that bad.

[rhandwor]

Pull the vacuum hose on your pressure regulator if its leaking replace it as with high vacuum its pulling fuel into the intake. I seriously all your injectors are leaking.