Need help with 2007 Ford Taurus SE - fluctuating RPMs at idle

2007 Ford Taurus SE - 108,000 miles

It just had a transmission fluid exchange and radiator flush; gets regular oil changes; has a fairly new battery; often gets fuel injector cleaner additives with gas fill-ups. I've replaced the camshaft synchronizer, fuel filter, idler pulley, belt tensioner myself within the last 2 yrs. It's got a new alternator and had a tune-up a couple years ago. It's paid off so I'd like to keep it running for as long as possible. The heatercore is bad (I believe since the heater doesn't work and I've seen fluid in the passenger side floormat - which is a common sign, right?), but that's quite a project... too expensive to pay for, and I need the time and space to do it myself.

So anyway, this idle problem has been going on for years and I thought I would've fixed given all the parts I replaced. I also replaced the idle air control valve, which didn't fix the problem, so i removed it and took it back.

Symptom - while idling in park or in drive (@ 800 RPM), the RPMs will consistently dip approximately 100-200 RPM. What are the possible diagnoses?

a reply to: six67seven Could be a small vacuum leak. Check your vacuum hoses for cracks and holes, Even a pinhole would do it.

a reply to: trontech

What's an easy way to locate holes in hoses?

Spray cleaner with engine on?

Take off your mass air flow sensor and soak it in 91% isopropyl alcohol over night. The next day, gently wipe of the deposits with a cotton swab. I did this to my girlfriends 02 Taurus and it was easy to do. I would start there to eliminate the easy stuff.

a reply to: six67seven That might work, just remember the fluid will be sucked into the hose. There probably is a better way. Just have to wait for someone more experienced to reply.

originally posted by: trontech
a reply to: six67seven Could be a small vacuum leak. Check your vacuum hoses for cracks and holes, Even a pinhole would do it.

This! I'd also use a cleaner (Safe for your car) in the gas tank to clean out any gook in your engine.

Thanks for the replies thus far. I'll get to work and post the results.

probably your idle air control valve ( IACV)
you said you had a radiator flush, well radiator fluid flows through one chamber the IACV and is separated from the air chamber in the IACV by a gasket.the radiator flush might have damaged the 8 year old gasket causing a small leak allowing radiator fluid to leak into the air intake chamber of the IACV.

ETA: I just noticed you said you replaced the IACV and then put the old one back on, did you replace the gasket?

Try unplugging the wire harness from the IACV, with the IACV unplugged the idle should increase and stay high.

I don`t think it`s the MAF sensor or you would have noticeable problems not just with idleing but also when you are driving.
don`t use carburetor cleaner on the MAF sensor it`s too caustic it will kill it.

also check the EGR valve make sure it is closing all the way and the vacuum hoses aren`t leaking, the EGR valve should only open at high speeds.

I had the same problem with an '03 Ford escort. Got the vacuum tubes replaced and the problem was still happening. So my brother and i got underneath the car and saw that my exhaust had a large hole in the pipe real close to the front of the car. We replaced the pipe and that fixed the problem

I say clean the mass air flow meter too, you can also use a can of carb cleaner to clean it. That worked on my 95 Taurus.

Curious what the fuel rail pressure is. Maybe a vacuum leak at the fuel pressure regulator? I was going for Idle Air until I read that you tried that. I have a tire pressure gage with a 3/8 hose connected to it. I pull the valve core out of the valve on the fuel rail and connect the line to it and place the gage under the wiper blade. Be careful, rail can be under a little pressure and spray fuel in your face.

I'm finding out that cleaner spray on hoses to look for leaks is a bad idea due to possible fire, especially with a hot engine. So first, I'll clean the mass air flow sensor and work from there.

a reply to: six67seven

Do you have a check engine light? If so read the codes to get some idea of the target problem area.

Sadly there are a bunch of possible issues on the wandering idle. Vacuum being the likely one I think.

Check the PCV valve and hose.
www.youtube.com...
Have a peek at other vacuum hoses, especially the connections that typically heat up and cool alot and age faster. Pull them off and put back on. If the hose isn't snug on the nipple it isn't going to provide vacuum.

Another one is the MAF sensor, could be dirty or slowly going. You can buy a special cleaner, nothing else is safe apparently, and try that.

And yes, leaking in the passenger floor is the heating core. Don't run the heater and it won't leak generally. The guy in this video tells you how to do it in 1.5 hours instead of the 5 hours everyone says it takes. No dash removal. Watch the vid and you might feel more comfortable to give it a try.
www.youtube.com...

Good Luck!

I remember when I first got my truck, I had an idle problem, it would sit at around 900 or so then dip down to almost stalling, and when I was driving and coming to a full stop at a light or stop sign it would do the same and even completely stall, it was very annoying. I scoured the internet looking for similar issues, it wasn't very common, and I got all sorts of fixes.

Finally I took it to my mechanic and he suggested a few things, tried them out, didn't work.
Then I remembered one time when I was working on my summer car I forgot to tighten the throttle body cable to it's proper tension, and I was getting somewhat the same issue. So I took out the throttle body from my truck, noticed it was very dirty, cleaned it all up tightened all the screws lubed it with the proper lubricant and it fixed the problem.
Not saying this is the fix to yours but it might work, and it's easy to do.

a reply to: Banquo
good suggestion.

an exhaust leak between the engine and the oxygen sensor will usually cause the engine to run rich which will affect the idle.
It could be the O2 sensor itself is malfunctioning and giving false readings causing a rich condition.

Like mentioned several times before its most likely the mass fuel sensor. I have the same make but mine is older but it's a common problem. Take the car to a local parts store and have them put a code reader on it. Usually it's free and they'll tell you what the computer says it is.

Just cleaning it may not be enough, it wasn't for mine, you may have to buy another one. I bought the cheapest one online and 5 years later it's still good.

a reply to: noeltrotsky

I've seen the 1.5hr heatercore replacement vid. Definitely the way to go for that problem.

Check engine light isn't on, but I need to check the PCV hose. I hate this location under the hood... so tight, but could be worse I guess.

Got the MAF sensor out. Noticed they are $130 to replace, so gonna head to the store for cleaner.

Stay tuned.

a reply to: six67seven

The problem with the cleaner is you don't know if it 'worked' or not...so if it didn't, like 9 out of 10 times it won't...you're stuck still not know if the MAF is any good.

Grrrr...sometimes just replacing it is best.

a reply to: noeltrotsky
ok, so i use starting fluid to check for vacuum leaks...small bursts in each area with hoses, or intake gasket area while the car is running....never had it catch fire. also be careful cleaning the maf, use cleaner that says mass air flow cleaner, some cleaners leave a residue on the maf, and when the elements heat up in the maf when the car is running, it will burn your maf up. just wanted to share some precautions with u, good luck!

a reply to: noeltrotsky

You can check it pretty easily with a cheap multimeter. A few different tests should tell you if it's bad or not.

A good explanation, here.