Suggestions for fluctuating park/neutral idle

[manimal]

Our 95 starts every time and runs great, tons of power for a V6 truck with 200k, etc. Still gets good mileage and recently averaged around 22MPG on a trip across state, even though multiple mountain passes were involved.

However once it has reached operating temp and is idling in neutral or park, the idle pattern is annoying. Every 5-6 seconds or so the idle will drop and fluctuate slightly before raising again to a normal, smooth idle. It will often continue doing this until the truck is placed into gear - idle is PERFECT in gear. While in gear, you could idle at a stop light forever and the idle will hold steady at a normal RPM.

It sort of acts like an accessory load is placed on the engine, e.g. power steering or A/C compressor kicking in - but neither of those things are going on.

Recently I have cleaned the IAC, MAF, and DPFE sensor has been replaced several times in the past. Spark plugs have not been changed recently but I would say are likely no more than 20K old - this issue has been ongoing for some time. No codes thrown, no indication of vacuum leak or any other common issue - though I have never re-torqued the intakes and I should likely give that a shot.

Truck also seems to have a leaky injector at times and will sputter after it has been shut down for 30 mins or so while hot, but runs normally after revved a bit to burn off any excess fuel. After that, runs fine. Never happens when cold. Seems to me to be a separate issue and a minor annoyance.

Any ideas?

 

[gatzdon]

Sounds like Engine Coolant Temp Sensor (engine perpetually remains in cold mode because it doesn't know the engine came up to temp).

Since you have a 95, I don't know what options are available to you to pull any Ford codes from the vehicle or see the engine temp value in the PCM.

If you google it, there is a chart of the common values for resistance versus temperature for Engine Coolant Temperature sensors. Should be easy to pull the sensor and check if the resistance is the correct value.

You can also check if the voltage to the sensor is correct as that would also impact the temp reading.

 

[gatzdon]

If you can get at the sensor easily, you can check the resistance value without pulling the sensor.

You may not have a leaky injector. Running in cold mode while the engine is hot will cause the symptoms you are describing.

 

[manimal]

OK, I'll check it out. I may actually have a spare ECT sensor.

 

[gatzdon]

OK, I'll check it out. I may actually have a spare ECT sensor.

Just remember that there are two temp sensors. One for the gauge, and one for the PCM. It's the one for the PCM that you want to check.

 

[Runnin'OnEmpty]

And the one for the PCM is the harder one to reach.
It's the one on the driver's side.

 

[manimal]

Bringing back old topic here.

Due to recent radiator tank failure, I ended up replacing the radiator, thermostat, and replaced the ECT sensor while everything was out of the way. Also reset the PCM by disconnecting the battery for quite some time.

Unfortunately this did not resolve the idle issue. Still occasionally drops/fluctuates idle once hot on a interval of around ~5-10 seconds or so.

Still having the issue with truck stumbling or wanting to die occasionally when restarting after sitting for short periods, with engine hot.

Going to check spark plugs soon, and will check running fuel pressure and hot start fuel pressure.

I think I may remove and fully disassemble the IAC, and make sure to get at the inlet filter discs - these have never been cleaned or removed, and the IAC has exhibited the hot whistle in summer time before, which will usually stop if you rotate the cap..

Truck rolled over 200K miles last month and other than this issue, still runs like a top.

 

[Turdle]

When you clean the IAC, use a small tool to actuate the internal plunger rod to it's maximum movement while spraying the cleaner. I think this might be hanging up inside your IAC and causing the idle issue.

 

[J_C]

I think I may remove and fully disassemble the IAC, and make sure to get at the inlet filter discs - these have never been cleaned or removed, and the IAC has exhibited the hot whistle in summer time before, which will usually stop if you rotate the cap..

Truck rolled over 200K miles last month and other than this issue, still runs like a top.

I wasn't aware that the IAC could be disassembled. I mean (IIRC) mine looked like the metal shell of the solenoid was formed (mechanically bent in a die) around the cast piece and it wouldn't be reasonable to try to pry it apart then hammer it back together.

Anyway I second Turdle's thought about moving the plunger around, and when I did mine, I set it on its end, put a drop of oil at the base of the shaft on the bearing, and worked it up and down a few times to get the oil into the bearing some, leaving it sitting in a propped up position so gravity would continue to work oil down in.

You mentioned that whistling stops if you rotate the cap. When you cleaned it did you take the cap off and clean out the felt filters in the cap? To check filter state you might pull the cap off while it's cycling the bad idle situation to see if that makes a difference, being careful not to lose the filter pads in the process as they aren't secured in, just loose friction fit on mine.

 

[manimal]

I have fully disassembled the older EEC-IV units, but I don't believe they are 100% the same. Regardless the valve housing is easy to remove & clean, just have never got around to it. That is the next thing to work on.

 

[gatzdon]

Just curious, did you actually connect to the PCM and see that it's actually going into closed loop for the fuel control? What value did the PCM report for Engine Coolant Temperature.

If the fuel control stays in open loop, that's your starting point for what to inspect. Read up on the conditions required for closed loop and check each system for proper operation.

 

[manimal]

May have been an ignition issue. Pulled the plugs and 4/6 were blown out to close to .080 gap. Multiple plug wires broken, and one of the plugs' terminals even broke off in the plug wire. Had to grab several wires off of my 91, and ordered a new Bosch set from Amazon.

Idle is significantly smoother, and obviously the truck runs much better now.

My dad had the 95 for years, I thought he changed the plugs a few years back. Guess not.