Power Surging Idle Help

[Pauliejr]

I have a 97 explorer stock (motor wise) 4.0sohc.

When I am at an idle or sitting at a light the motor have a surging idle. It is not a random jump but a very persistent idle surge slightly dropping then catching itself every 2 seconds or so.

When this happens the battery meter twitches and so do the dash lights.

i have tested my battery once when the car was running and it was reading over the 12 volts. I am not sure what the issue is but I really want to solve it ASAP.

The truck also sometimes seems to bog down a bit or have a delay when I get on it and in the morning on a cold day when I crank and start it up it cranks fine but once it fires up it drops rpm all the way down almost stalling then goes to the regular idle.

Please help with any Uggestions and how to check on it.

 

[2000StreetRod]

battery voltage?

What is the battery voltage when the engine is idling? It should be around 13.6 volts or more.

How low does the idle speed drop to when in Park or Neutral? It should be about 650 rpm when the engine temperature is normal (190 degrees F.). It should be faster when the engine is cold. The idle speed is controlled by PCM and the idle air control valve (IACV).

 

[Pauliejr]

Let's say it's idling at 650-700 is very minor drop the needle flutters and u can hear it kinda fluctuate in idle sound. It doesn't die it just sounds like a very rhythmic in even idle every 3 seconds. Not a random flutter or sputter. Also on a cold day her 20 degrees I start the truck it fired up and then dies. Only the first time then I start it again and it's fine.

 

[2000StreetRod]

DTCs?

Are there any diagnostic trouble codes?
You didn't answer my question about the battery voltage.
Have you tried cleaning or replacing the IAC valve?

 

[Pauliejr]

I will get a voltage reading today after work. And no I have not tried that yet. Did not want to do anything until I have a solid lead

 

[Pauliejr]

I also noticed it does it more when I put the car in drive or reverse with my foot still on the break. Rather than in park if that helps.

 

[Pauliejr]

So with the car off it reads a steady 12.7 no movement. With the car idling it jumps around between 14.20-14.01 and constantly jumps between that range. 14.05 14.08 14.19 14.15 yada yada. I also cleaned my iac with contact decreased and it do nothing.

 

[2000StreetRod]

probably not battery or alternator

With those voltages your battery is probably good and your alternator is functioning properly.

Does your check engine light work? It should come on when the ignition is switched on. Does the check engine light stay illuminated when the engine is running?

If you had access to a scan device you could read the commanded idle speed and the engine rpm and determine if the IAC valve is slow to respond to the PCM's command. You could also monitor the fuel trims to determine if the engine is running rich or lean.

If the upper and lower intake manifold gaskets have never been replaced they are probably dried out and shrink with the cold letting unmetered air enter the intake manifold. That results in a lean condition. Broken intake hoses can also cause a lean condition. The only reliable test to detect intake manifold vacuum leaks is with a smoke machine.

If there is black smoke coming out of the tailpipe then the engine is running rich. That could be due to a non-functional engine coolant temperature sensor.

How long has it been since the spark plugs and wires were replaced?

It is very difficult to isolate to the source of a problem with only knowing the symptoms. Testing is required to avoid unnecessary replacement of components.

 

[mark2016]

I have a 97 explorer stock (motor wise) 4.0sohc. When I am at an idle or sitting at a light the motor have a surging idle. It is not a random jump but a very persistent idle surge slightly dropping then catching itself every 2 seconds or so. When this happens the battery meter twitches and so do the dash lights. i have tested my battery once when the car was running and it was reading over the 12 volts. I am not sure what the issue is but I really want to solve it ASAP. The truck also sometimes seems to bog down a bit or have a delay when I get on it and in the morning on a cold day when I crank and start it up it cranks fine but once it fires up it drops rpm all the way down almost stalling then goes to the regular idle. Please help with any Uggestions and how to check on it.

Is your Heat/AC/Vent set to on or off? When on in any setting but the first for upper vent it will cycle your AC compressor which can make a slight regular variation.

 

[Pauliejr]

Since the iac cleaning it's gotten a bit better and with the blower in the off position it's actually not bad at all. Is that normal or did I isolate the issue.