Sudden idle drop

[asenna]

When I am stopped or at very low speed my car has begun to suddenly drop idle. It shudders a bit but has never quit on me. I am wondering if it maybe happening when the electric radiators fan comes on. It doesn't actually affect the cars drive-ability.

Little worried it's a sign of impending failure and I'll get stuck somewhere on the side of the road. It's a '91 Ford Escort 1.9l.

Any suggestions much appreciated.

 

[BlazerLT]

Do you have the defrost on when this happens?

 

[acranox]

what's the RPM of the engine normally, and how low does it drop?

 

[moribundman]

Is the idle RPM just dropping below normal, or is it hunting? It could be a vacuum, leak (vac hose, gasket at intake manifold, throttle body, plenum, etc), or it could be a dirt or defective idle control valve. Not sure if an Escort has an ICV. You may also want to make sure that all spark plugs and park plugs wires are in good shape.

 

[Ugly3]

quote:

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Originally posted by asenna:
When I am stopped or at very low speed my car has begun to suddenly drop idle. It shudders a bit but has never quit on me. I am wondering if it maybe happening when the electric radiators fan comes on. It doesn't actually affect the cars drive-ability.

Little worried it's a sign of impending failure and I'll get stuck somewhere on the side of the road. It's a '91 Ford Escort 1.9l.

Any suggestions much appreciated.

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Bet it is the fan or A/C going on.

 

[punisher]

Even on a good day the 1.9 is a rough idling engine.

Verify there are no vac leaks as suggested above, a loose vac line is common. The IAC and throttle body do get sludged up. You can use carb cleaner and a brush in the throttle body and either remove the IAC and clean it or spray carb cleaner into the IAC air intake hole in the throttlebody while the engine idles.

Also something to consider, has your battery run down recently? A dead battery will cause your PCM to lose it's memory and idle speed settings. It can cause the same symptroms you mentioned.

 

[asenna]

"Do you have the defrost on when this happens?"

Yes I have been using the defroster.

"Is the idle RPM just dropping below normal, or is it hunting?"

Not sure what you mean by hunting.

I am at a stop light say, the engine is at it's normal idle and suddenly the idle drops and the engine runs a little rough. The drives as normal however.

I have had the cars for years never done this before.

No A/C. Fan not making any unusual sounds.

I clean the throttle body at least once a year. When dirty it creates a rough idle - this I know.

Left lights ons and drained battery once but that was a while ago. This rough idle drop has been going on for several months.

 

[yugrus]

Using defroster implies that your A/C cycles on and off. Hence the intermittent RPM drop and the engine "roughness". Turn off your defrost for a day or two, you'll see the difference.

 

[moribundman]

quote:

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Not sure what you mean by hunting.

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At idle, does the idle drop, then bounce back just to drop again, and so on? If the idle dips only momentarily, for example when you turn on the lights, roll down a power window, or if the A/C comes on, it's normal. If the idle RPM is all over the place, something's wrong.

 

[asenna]

The idle seems to be running a little high when I come to a stop. Then after a few seconds it just drops to a much lower idle and stays there.

As I said the car drives normally and at the low idle, just as it drops, it seems to run a little rough.

The idle drop does not seem to be afftected by turning on the radio, defroster or lights.