RPM Drop and Click, Assoc with heater

[SkyOutGirl]

I have a 2001 Explorer Sport 4wd (w/broken 4wd )

This started by just having a rough idle; acceleration and driving didn't have any problems. Then the rough idle turned into a bit of a vibration, like a shiver running through the car. Not constantly, but in a (probably timable) rhythm. Then the click started happening (this is all over like a 6 week progression). I noticed it while outside my car one day while it was running. The idle would get rough and drop and there was a fairly loud click at the lowest idle point, then the idle would go up again. This was with the same type of timing (maybe 20 seconds between clicks). I started to watch my RPM's while this was going on, they typically idle about 600. Right now, at the worse point, the drop is going all they way to 200 before the click and the RPM's climb again.

The other part is I started to notice it doesn't really happen (or at least not nearly as aggrevated) when the heater is off.

The other day for the first time I felt the lag in RPM right when I tried to accelerate and it was quite sluggish, but recovered quickly in that timing cycle. Normally I only feel the shiver and click while at a stop.

Someone mentioned coolant levels, so I checked the level and it looked fine but was obviously in need of a flush and fill. So, I got that done yesterday and it didn' help the problem at all.

Any ideas?

[denisb]

If it was summer I'd be tempted to say your AC compressor is on it's way out and when your AC clutch kicks in it's bogging everything down. I'm not sure where your located, so it's still possible you're using your AC (If your not her in fridgid Canada). The AC clutch would cycle at intervals similar to what you are describing and I've herd of people have there AC compresors lock the fan belt pretty well up.

Denis

[shorod]

Well, you may be on the right track. If the ambient temperature is above freezing and the Explorer either has the electronic automatic temperature control, or she is using the defroster, he A/C compressor is likely still engaged. If the A/C is kicking in and the Idle Speed Control (ISC) is not compensating for the added load properly, then she might experience symptoms like SkyOutGirl described.

When was the last time the Explorer had a tune up?

-Rod

[SkyOutGirl]

I am at 107000 miles, and I had a 90,000 mile tune up done at around 95000. I think that was sometime near the end of the summer.
I am in Salt Lake City, and it is about 15 degrees here in the day.

Oddly, I didn't notice the problem this morning on the way in to work while my car was cold or when it had warmed up.

A friend mentioned to try replacing the plugs and wires. I think the spark plugs were replaced at my 90,000 tune (those things are expensive!)...I am not sure if they replaced the wires. The other suggestion I got was the distributor cap...?

[shorod]

I don't think your 2001 has a distributor cap, it should be distributorless ignition.

A true "tune up" will include spark plugs and spark plug wires, as well as the fuel filter, air filter, etc.

One other question, does this seem to happen more when the head lights are on? I wonder if your battery and/or charging system is getting weak. Maybe under heavy electrical load, the system voltage falls low enough that the PCM has difficulty functioning properly. When using the heater, you typically have the blower motor turned up (load) and at a stop, your brake lights are on (load). If the system voltage falls below 10.5 volts, the PCM may start operating in an unreliable state. The clicking you hear may be the PCM triggering relays, or relay coils dropping out due to low voltage.

-Rod

[denisb]

Good call Rod. My Taurus was acting similarly for a couple of weeks before the alternator in it went south. That would be worth a peak into.

Put a voltmeter on your battery terminals when the car is running and turn everything on the vehicle that draws current (Radio, lights, heater, etc) and see how much your voltage goes down. Even under load, I would say you should be getting 12.5 to 13v at least.

Denis