First, I love FTE and usually get what I need without a post.

'94 Ford Explorer 4x4
160,000 miles
V6, Automatic transmission

I have done lots of light repair on this vehicle (emergency brake cable, tune-up, oxygen sensors, brakes, lift gate piston, interior door panel, window motor, etc.) but am perplexed with my current problem:

When the engine is put under load, it surges. I.e., when you shift from park to drive or reverse OR from neutral to drive or reverse, the engine revs to about 1,200 rpm. ( I fear my u-joints will not last very long unless I correct this.) The engine also revs in park or neutral when you turn on the AC. When you shut it off, the idle returns to normal. The idle is erratic (high and low) from time to time.

After the surge, if you wait several seconds, the idle drops back to a more normal level. When decelerating, the idle seems to 'stick' high, as well, so rolling up to a stop sign can be a little tricky as the engine, in gear, remains at about 1,200 rpm. I've been shifting it into neutral as a work around, but it's clearly not a desirable solution.

I have replaced both O2 sensors, (carefully) cleaned the MAF and replaced the IAC and TPS. Mileage seems to be low (about 12-14 city, I remember it being higher) despite recent new plugs and wires. The engine shows no signs of weakness. Current codes are (KOEO) 214 - Cylinder ID circuit failure and (KOER) 411 - Cannot control RPM during KOER low RPM check.

I'm thinking vacuum, but the local shop tested and claims no issues.

Many thanks in advance for any suggestions or observations.

-Darrell

 

Was the code 411 prior to replacement of the IAC?

Have you checked the throttle plate to make sure it is able to close completely? You might have a carbon build up on the back side that prevents the throttle plate from completely closing effectively, preventing the IAC from doing some of its job.

When idling with your foot firmly on the brake and the transmission in gear, is the engine smooth? How about during light acceleration, any signs of misfire?

Have you checked the fuel pressure or ever replaced the fuel filter?

-Rod

 

Many thanks, Rod...

411 both before and after new IAC.
Have not inspected throttle plate, but will (clean with carburetor cleaner?)
Engine smooth when idling in gear, foot on brake.
Accelerates like a banshee, no issues or misfiring.
Have not checked fuel pressure or replaced the fuel filter, that I recall.

-Darrell

 

Daring -DO NOT USE CARB CLEANER ON THE THROTTLE PLATE - the solvents in carb cleaner are harmful to your intake plenum - get throttle body cleaner.

 

I've been very pleased with STP Throttle Body Cleaner. It cuts through the gunk quickly and evaporates better than some of the more expensive brands.

-Rod

 

Got it - no carb cleaner on the throttle body. Don't have any on the shelf, have to hit the store. Curious if this could be solved this simply. Still need to inspect....I'm looking for caramel colored build-up, I suppose. Will take a picture and post.

 

What you're really looking for is a throttle plate that isn't completely closed with no pressure on the accelerator pedal. If the plate appears to be closed completely, open the throttle plate either by the cable pulley or by someone pressing the accelerator pedal and inspect the back side of the plate. If it is coated with tan, brown, or black carbon build up, that's what you want to clean off with the throttle body cleaner. Of course all this fluid will make the vehicle nearly impossible to start unless it sits for a couple of hours first or you hold the throttle wide open while cranking the engine in spurts. This puts the PCM in Wide Open Throttle (WOT) Clear Flood mode, shutting off the injectors so as to not add more fuel to the already saturated cylinders.

Ideally you'd remove the spark plugs, apply rags to capture the fluid from the plug holes, then crank the engine a few times to remove the excess cleaner. Then install the plugs and all will hopefully be better. The engine will probably run roughly for a minute or so until it burns off the cleaner.

-Rod

 

Shorod, all:

I'm back from vacation, back to the mystery of the Explorer with a mind of it's own.

My $3 investment in a can of throttle body cleaner produced a cleaner throttle body, but the problem persists. I don't think I accurately described the problem by saying the idle was 'sticky', as a matter of fact, I may have misled:

The issue, if I could try to explain it once more, is that the idle is normal and smooth when there is no load on the engine. As soon as load (shifting into any gear or putting the AC on) is applied, the idle speed increases to approximately 1,200 rpm for 30-45 seconds, then, gradually decreases to a more normal 800rpm.

When decelerating, in gear, say, off the freeway, the engine idle sits around 1,200 as you approach a stop (the engine is pressing forward while you are simultaneously trying to slow it down). I shift out of gear to work around the problem; when it's not engaged in gear, the idle is completely fine.

Assuming it is completely unrelated, I suspect the ABS pump has gone bad - the ABS is engaging erratically and the light comes on regularly, but doesn't stay on all the time. Anyway, thought I'd mention this.

Suggestions on next steps?

-Darrell

 

I continue to worry about this being a vacuum problem (cracked hose?), mostly because I have no idea how to test/troubleshoot/isolate this condition.

 

That $3 can of throttle body cleaner could help you isolate a vacuum leak if used carefully since the cleaner is flammable. If the cleaner is sprayed in the area of a vacuum leak, the leak will suck in the cleaner and cause the idle to briefly change.

You might also try turning the A/C on or off and see if that has an effect on the idle speed. You could also try turning the steering to one of the locks and holding it there for only a few seconds. Does that cause the idle speed to drop? If so, the Idle Air Control (IAC) servo may be slow to respond.

As for the ABS issue, I don't think you have a pump issue. It sounds more like you have an issue with one of the wheel speed sensors or tone rings. Either of these would be much less expensive than an ABS pump.

-Rod

 

Will try spraying vaccuum lines to test for leaks (idle changes), still not sure if a vaccuum leak would cause this problem. Is there any kind of sensor or control logic that signals the engine to increase rpm based on load (like shifting into gear)?

 

Many times the application of volatile spray will not disclose the vacuum leak.

I finally manufactured a smoke injection machine 3-7psi (adjustable), Amazing when you see the wisps of smoke indicating the leak/leaks.

 

Update!

After establishing a habit of shifting out of gear when rolling up to a stop, I finally got out of the car a couple days ago and yanked the plug off the IAC just for *****s and giggles: Problem gone, but now I'm not using an IAC. Is this an issue?

Do I go back to square 1 and see if I can clean it up/repair it or just buy new?

I'm a little embarrassed as I wrote initially that I had bought a new one and the problem persisted; while that's true, something else must have happened between then and now.

Sheesh.

-Darrell

 

Yet another update, oh gurus, I hope you'll come to my rescue.

The Explorer problem persists. I removed the IAC and the problem goes away, so I figured the IAC was bad. Bought a new one, installed it, same damn problem.

Used a whole can of spray trying to detect a vacuum leak (idle speed changes), probably ruling out the vacuum problem now.

Just went back and read the two problem descriptions, they're spot on.

Hmmm. I wonder if I simply have the idle set screw set too high? I don't think that accounts for the surging I'm experiencing.

What about timing?

Thanks in advance for helping me narrow this down...

-Darrell

 

If you have turned the throttle stop screw, that was your first mistake. That screw does not need to be adjusted for the life of the vehicle, and contrary to popular belief is NOT used to adjust idle speed. It is there to adjust the closed position of the throttle plate only. Idle speed is completely under the control of the PCM and is not user adjustable. To set the hard stop, with the key on and engine not running, carefully probe the three wires at the throttle position sensor (do not disconnect the connector.) One of these wires will have a voltage close to one volt. If it is not very near one volt, adjust the throttle stop until the voltage is 0.95-1.00 volt. Disconnect the battery for five minutes then start the truck and let it stabilize. If the idle speed is not correct, continue to look for problems elsewhere but DO NOT change the stop screw setting. If the throttle position sensor is not within that range, the PCM will change into alternate running modes because it believes the throttle is open, resulting in erratic idle, high idle, etc.

Timing is not adjustable on the 4.0L.


Jay