I have a '97 Taurus 3.o V6 with a strange idle problem. It runs fine but it seems to keep accelerating slowly with my foot OFF the gas when traveling along a flat road or in a residential 25 mph area, I actually have to brake slightly in slow zones. What I noticed the other day is it's almost like having the cruise control on in the city. I popped it into neutral on the freeway the other day and the idle stayed at about 2500, I did the same thing slowing down on an offramp and the idle went right back up to 2500 but if I come to a stop in gear then put it into neutral it idles just fine, around 800+ or so. I and most others who drive this thing notice that it coasts really easy but now I know why, the idle is way up when moving. Seems to me that the EFI is supposed to shut off when decelerating or going down-hill against compression after so many seconds but that ain't happening.

I didn't get any codes last time I checked and this thing has done this since I've had it (about 2 years), I don't drive it very often and just really noticed the problem recently. Other than that it runs great and is used mostly for long-distance trips.

Ideas??

TIA

JohnF

 

I would suspect the Idle Air Control (IAC) valve which is responsible for maintaining proper idle under all conditions, including decleration.

 

I replaced the IAC with no change in the symptoms. RPM stay high when I let off on the freeway and if I shift to neutral the tach shows as much as 2200 RPM until I get nearly to a dead stop, then it starts dropping towards normal. I tried disconnecting the IAC while it was idling and it nearly died. I just read something about the mass air sensor but it doesn't completely match my symptoms

Any other ideas?

JohnF

 

Have you examined the throttle body assembly and cable while someone inside the car duplicates the concern? What I'm getting at is that, there might be an issue either with the throttle cable or with the throttle body itself, to the effect that the throttle plate is not shutting all the way closed when you let off the accelerator. If the throttle plate is getting hung up for some reason, then the desired 'closed throttle" condition would be delayed accordingly (you should examine the accelerator pedal linkage for the same reason).

Along the same lines, the throttle position sensor (TPS) is responsible for telling the computer what the throttle plate is doing (open, shut, part throttle, etc.). They rarely fail, but at this point you have to keep an open mind.

 

Same car basically same problem.I replaced the tps and didn't help.Mine was fine until I unhooked the battery. When I hooked it back up the idle went high.Would cruise without touching the gas.Unhooked the bat again for a couple hours and hooked it back up. Went back to normal.When I unhooked it again to replace the starter,I went through the same bull.It won't go back to normal.I unhooked the IAC and it idles about where it's supposed to.Start to think the pcm is bad.

 

Air bypass valve.

They wear out over time, and generally get stuck further and further open. Its an electric motor driven valve.

The eec will compensate for it, and there you go....

(it happened to mine)

When you don't believe anything else, and the idle gets to be around 3K RPM try it. It will save you mass "Q's" of cash to change it yourself.

I remember tapping the throttle as if it was a stuck carb linkage and the dirty rotten thing would just keep on revving higher and higher...

Sometimes better ideas are a pain in the backside....

 

I believe what you are refering to as the air bypass valve is the IAC (Idle Air Control or something like that). I replaced that already. It was something like $45. at the auto parts store. Still no change over all. It runs OK sometimes and idles down as it should but most times the idle is way high. After warmup it will sometimes idle up around 1200 and drop, with a clunk, to 900+ when in gear, other times it will be around 700 or so in neutral and drop to about 600 in gear. The pain in the a** is driving in traffic, it usually wants to either stay at the same speed I was running and I have to brake to skim a couple MPH off or, in the city, I have to brake all the time because it wants to run at 45MPH when the limit (or traffic) is running around 30 MPH or less. When it's really acting up ( and I'm pissed off at it) I drive in low on city streets and will run the RPM up to 4000 sometimes just to keep from constant braking. All the vatos here in Phoenix think I want to race then (an old guy in a 4 door Taurus GL ????). Even that doesn't give me all the compression braking I should have.

JohnF

 

FWIW, when the ECT on my 4.0L failed, it adversely affected the idle, it would wander up and down and would often race when I came to a stop. That's because, if the computer thinks the engine is cool, it will keep the idle high.

Along the same lines, other things that affect idle like that are the power steering and air conditioning systems. There is a PS pressure switch that tells the computer when there is an increase in system pressure. The computer in turn raises the idle to help prevent stall. Same thing happens when the A/C compressor is running....the computer kicks up the idle in order to keep everything flowing at suitable rpms.

The thought process is as follows: maybe the computer is getting a signal from somewhere causing it to raise the idle unnecessarily.

 

I sorta mentally eliminate the ECT because the thing get's terriffic mileage, I got 31 mpg Phoenix to Yuma running just over 80MPH last time, and if it thought the engine was cold it would run rich. I didn't think about the power steering switch though. I'll be back in San Diego this weekend so will have access to my OBD reader. I'll see what that tells me.

JohnF

Factoid; Phoenix, Az. is about 1200 feet above sea level (!). It's a steady ramp downhill along the I-10 to 85 to I-8 route in to El Centro Ca. which is a few feet under sea level. Yuma, Az (at the Az/Ca. border right on the Colorado River) sits at about 200 feet.

 

Hi @johnfl did you ever find why it was happening. I have the same issue happening to me. When I start it, the rpm ramps up to 2500, and idles around 1100 however, while cruising it feels like it is giving gas and while slowing, I have to press the brake really hard since engine rpm is high, it also causes erratic shift from 2-1 when this happens. I realized it starts happening when the car gets warmer. Please let me know if you found the solution. This is the 3.0 v6 ohv engine.

 

​​​​​​It's safe to say he probably doesn't own the car any longer since he posted that 18 years ago.

 

Thats correct but maybe he remembers how he fixed it if he ever did. You think its a better idea to open a new thread?

 

Yep. That way nothing gets lost in translation.

 

he has not logged on in over 3 years, so dont hold your breath looking for a answer.

 

Damn, long time ago.......
It was stolen. BUT, I did find that the big electrical connector on top of the tranny was dirty. Pulled it apart, sprayed it out with contact cleaner, smeared some dilectric grease in there and happy days were here again... until someone else needed it more than I....along with my golf gear and camping bag...and tools.