Idle Dropping/Almost Stalls in Traffic

[BrandonVA]

I've noticed lately that when I am in stop-and-go traffic that my idle will drop to zero on the rpm guage and my car will almost stall. It has not actually stalled yet but if I press the gas when the car is doing this it will have no power so this is not ideal in a heavy traffic environment... I have recently replaced both downstream oxygen sensors, tps sensor, iac valve, egr valve, spark plugs, coils, and I've done lots of amsoil/redline fuel treatments. Any idea what could be the culprit here?

this is on an 02 ford escape with 153k miles

 

[MichiganMadMan]

I've got to ask a couple of questions first before I narrow in on what is making it happen.

You list a flurry of parts that have been replaced, were these before or after the problem started?

Does it have the same (or nearly the same) behavior hot and cold?

Are there and P-Codes? Is the "check engine" light on?

Fuel economy is normal?

 

[SHOZ]

I'd recheck the connections. The ECU should command the Idle Air valve to maintain idle.

Fords are notorious for stalling like that though. Three Taurus I had all did that.

I bumped the throttle plate open just a hair with the throttle stop screw to stop it from happening.

Waiting for the YOU NEVER SHOULD ADJUST THAT SCREW chorus to chime in any minute......

 

[BrandonVA]

I replaced all those parts when I got the car (bought used). I never really had this problem until recently so I think it is unrelated to all those new parts I put in.

It does have the same behavior no matter the temperature. No codes or check engine light. Fuel economy.....i'm getting about 17.3 mpg. That seems pretty low compared to what I've heard some people are getting with the V6 escapes. I try to drive fairly conservatively. Could the bad fuel economy/low rpms be caused by a dirty MAF or upstream O2 sensors?


thanks for your input...much appreciated.

 

[SHOZ]

It won't show a code. It is just a lazy IAC.

Start the car and let it get to operating temp.

Turn the throttle stop screw in so the engine is running around 1200 rpm.

Unplug the IAC.

Adjust the screw back out until the engine idles around 450 rpm.

Turn the car off. Then plug the IAC back in. Disconnect the battery so the ECU looses it's learned idle. The reconnect the battery, start it up and let it relearn idle.

I never had a problem after that. This was a recommended procedure from SCT tuners.

 

[NHGUY]

Check for a bad battery and or battery terminals.Believe me,I have had that happen on 2 cars.If the battery is older it might be failing,or the battery clamp is not making good connection.

 

[NHGUY]

....car started fine,but when stopped it would stumble and try to stall.Replaced battery (or cleaned clamps) and problem went away.

 

[BrandonVA]

i did replace my iac a few weeks ago and never reset the ecu. i'll a reset and see what happens.

 

[440Magnum]

Sounds a whole lot like what 2000/2001 Jeep Cherokee 4.0s did due to vapor lock in the fuel rail when using winter-blend gasoline (which boils much more readily than summer gasoline). That was a known issue with them- several TSBs (none entirely effective). In this case, you'd think if it were common there'd be a TSB.

Other things would be checking the idle air regulator for plugging- but that wouldn't explain loss of power when you step on the accelerator.

 

[SwampSurvivor]

Originally Posted By: SHOZ
I'd recheck the connections. The ECU should command the Idle Air valve to maintain idle.

Fords are notorious for stalling like that though. Three Taurus I had all did that.

I bumped the throttle plate open just a hair with the throttle stop screw to stop it from happening.

Waiting for the YOU NEVER SHOULD ADJUST THAT SCREW chorus to chime in any minute......


I adjusted the idle screw up a bit on my '01 Taurus. By that time, I had stopped going to TCCA (I think I remember you from there), but I remember posts about that everywhere!

I adjusted it up a tad because it would light the oil pressure light at hot idle.

 

[Kool1]

Is the problem consistent or occasional?

 

[BrandonVA]

occasional

 

[fdcg27]

When I had this problem with my old BMW, it turned out to be nothing more than cracks in the boot from the airflow meter to the intake manifold.
A ~ $25.00 part and a ten minute job to replace and fix.
This may have nothing to do with what you're seeing, but what I mean to say is that you should check the simple stuff first.
A can of either starting fluid or carb cleaner will help in detecting any leaks not readily seen.

 

[Warstud]

First off.... why did you replace all those parts? And second what did you replace prior to it stalling.

 

[BrandonVA]

I replaced those parts because they were worn out. I think the car sat for a long time before I bought it. I don't think this is related to any of those new parts.


one more thing...if i step on the gas really hard when the rpms drop really slow I will hear/feel a loud clunk like the transmission is engaging. I don't know what's going on there.

 

[armos]

Quote:
will drop to zero on the rpm guage and my car will almost stall.

So your tach signal is disconnected from reality.

I don't spend much time with modern cars. But on older designs, the tachometer signal comes from the ignition system. On those, when a tach drops out it indicates a primary ignition failure.

I'm guessing that nowadays the tach signal would be taken from the crank position sensor. I don't know that but it makes sense. If so, I'd look there and associated wiring between it and the ECM. It's obviously not just on the gauge side or it wouldn't be trying to stall.

Whatever the reason, you're getting a zero tach signal on a running engine. Figure out why it's dropping out and the rest of the issue should follow.

 

[BrandonVA]

could a zero tach signal be caused by a cheap TPS sensor? I replaced mine recently but did NOT use OEM. I think it was Bosch or standard.

 

[Warstud]

What you describe sounds like you may be low on transmission fluid.

 

[BrandonVA]

it is not low on transmission fluid

 

[Propflux01]

Originally Posted By: BrandonVA


one more thing...if i step on the gas really hard when the rpms drop really slow I will hear/feel a loud clunk like the transmission is engaging. I don't know what's going on there.


Engine mount.