Contour Enthusiasts Group Archives Forums General Troubleshooting The low-idle blues

My car:

1998 Mystique
2.5 V6
ATX
~55k miles


Problem:

Recently, like for the past few weeeks (5-6) i've noticed that my car's idle speed has been sitting at like 500 RPM versus around 700 before. Also when i rev it up while idiling then let it come down on its own, the engine speed drops real low, like 300 or lower and sounds like its gonna die...however, it always catches itself, and has not died yet. Then a few days ago, the car started idiling real low, like 200, on its own...that freaked me out, so i shut her down. Now idle has returned to approx. 500 when i let it settle; when in "Park" or "Drive."

What i've attempted so far:

-I cleaned the IAT and MAF sensors with some non-residue electrical cleaner (basically for the MAF i just sprayed it on, it looked really fragile, and i didn't want to break it)

-Checked the EGR valve. I applied vacuum to it at idle and the RPMs bog down real hard...which leads me to believe that it is functioning fine. Also idle speed doesn't change at all when i disconnect its vacuum line at idle.
Also, in a related matter, i have recently replaced the DPFE sensor (and hooked it all up correctly) with a black plastic one, just stating this as an fyi. The problem was there before and after DPFE replacement.

-I cleaned the IAC valve with carb cleaner. I used plenty of swabs and cleaner; and made sure that the rod/valve moved fully, and that it was all clean. To test it out, i disconnected it at idle and the car almost stalled out... so i reconnected it quickly. This leads me to believe that the valve is functioning well.

-I have reset the pcm many times by disconnecting the battery for long periods of time, like over 10 min.

-I have also checked the vacuum lines at the EVR thing, around the EGR crap, the 2 lines on top of the UIM (the further front one actually comes out really easy)

- I just put in an SVT airbox with new filter, its all hooked up properly...anyway the problem existed before the new intake

...So, whats left to check?



Am i correct in assuming that if i had a vacuum leak that the idle would not just be lower, but rough as well?

I'm kinda confused, when i put my ear close to the PCV valve i could kinda hear rushing air at idle...could a bad PCV valve cause low idle?

Any and all help is greatly appreciated!





edit: Also, fyi, no CELs or warning lights of any kind.

Your IAC is still suspecious.

When it is acting up, pull the wire off the IAC. If the idle drops more, it is likely OK (although it could be sticking nearly shut but this is not very common). If the idle remains the same, it is probably the IAC. Sometimes they do not respond to cleaning. Although the PCM could be commanding such a low idle, it is highly unlikely.

Autozone has an new IAC for $67 (I have a '96 Zetec). Do you know anywhere else cheaper? And what is this I've read about replacing a gasket when cleaning or replacing? A new IAC out of the box should have everything I need, right? Thanks

Big Jim,

I tried the IAC disconnect thing before, but i tried it once more right now. When i disconnected it, the engine died.


Also, last night i changed the PCV valve, with a purolator one. And right after i started it up, it idled exactly at 750 for a while...then i went out for a drive and it started sitting at 500 again when i was stopped. Now it idles at 500 once more.

I don't know what else to do really.

Could a clogged fuel filter cause such conditions?

I bought a new one, and i plan on replacing it some time next week.

...Now the one thing that i really don't want it to be is a clogged cat. But is this a possible cause?
Sometimes under heavy acceleration/decelleration, i get a heavy sulfur smell...



I appreciate you replying, thanks.

It does not sound like the cat or the fuel filter would have any bearing on this.

A plugged fuel filter would cause problems when there is heavy fuel demand such as under heavy acceleration.

Also a plugged cat would be worse with high air flow through the engine. At idle, there is minimal air flow.

You might try putting the original PCV valve back on and seeing it it makes a difference.

A possibility is a vacuum leak of some sort, so that is why the wrong PCV valve is a possibility. Look for vacuum leaks in general. Look especially at all the vacuum lines.

It is probably a simple problem.

I had a problem where that I would be driving along and then the car would die. Could not start it for an hour or so.......This drove me crazy.....95 Contour 2.5L atx. I then was clued into the fact that when it died on the highway, my foot was off the pedal. Also it would die at stop lights. I cleaned my iac. Still could not find the problem....I finally replaced the iac since my problems were idle related. Problem went away once I replaced the iac. In my opinion cleaning does not do that much....After 100,000 miles or so, do yourself a favor and replace it. Why deal with flakey issues after 100,000 miles. For example my cam and crankshaft sensors are about 12 each. I replaced both of them just to be safe. I have 170000 miles on the car.

Regards,
Bob

I have a low idle problem on my other Contour when cold. Only when I put it in drive. It will almost die and then the idle comes up to speed. Once the engine warms up no problems.....I am starting to suspect throttle idle sensor but this is just a guess on my part.

IAC changed
ECT Changed
egr solenoid changed
vacuum harness replaced.
ignition pack replaced
wires and plugs replaced

Well when I put it in drive, and have the brakes on, the engine will almost die and then a few seconds later it comes up to speed. The car is not moving at all. I have replaced the tss and didn't make any difference. There are no vacuum lines running to atx. Only a load is placed on the engine since atx is in gear..... so I guess the question is what reacts to bring the engine back up to speed once the atx is in gear....