2002 Park Ave - Hunting Idle at Startup

[markfothebeast]

2002 Park Ave
3.8L N/A

I replaced the UIM and LIM gaskets, plugs, wires, MAF, coils, and ICM. It would only start if I held the pedal down but that went away after cleaning the EGR and IAC.

Now it starts much better but takes about 4 seconds to fire and has a "hunting" idle on cold start for about 30 seconds that eventually stabilizes. There's also a slight misfire on cylinders 3 and 6 but that might be the coil that I swapped in from another vehicle. There's no codes or CEL.

Any idea what might cause a "hunting" idle at cold start that goes away?

 

[Alan 55]

This is a long shot but here goes. Have you checked your fuel pressure with a gauge attached to the test port on the fuel rail? In the event that you don't have a fuel pressure gauge this may be available as a loner tool from one of the Auto parts stores. Concerning safety, please wear eye protection and avoid hot engine components such as the exhaust manifold with gasoline. The fuel pressure should be around 52-59 per my 2001 FSM. I suspect fuel pressure as you mentioned that it takes about 4 seconds to start. It seems to be lacking fuel pressure at the rail for an instant start.

 

[markfothebeast]

This is a long shot but here goes. Have you checked your fuel pressure with a gauge attached to the test port on the fuel rail? In the event that you don't have a fuel pressure gauge this may be available as a loner tool from one of the Auto parts stores. Concerning safety, please wear eye protection and avoid hot engine components such as the exhaust manifold with gasoline. The fuel pressure should be around 52-59 per my 2001 FSM. I suspect fuel pressure as you mentioned that it takes about 4 seconds to start. It seems to be lacking fuel pressure at the rail for an instant start.

Unfortunately my fuel pressure tester internals from the end magically fell out somewhere. So I had to remove the shrader valve on the rail and test it that way.

I had a little leak at the fitting so I didn't run the engine. But with key on, engine off, 50PSI. I did replace the FPR because it was leaking prior. Forgot to mention that.

 

[markfothebeast]

There could be a good possibility it is the pump. It's been sitting in old fuel and the sender is now making the fuel gauge go nuts.

 

[markfothebeast]

I found that the 3 and 6 ignition coil had no continuity ln the secondaries. I swapped it out. Still a slight misfire from these two cylinders and the fuel trim drops just slightly negative; roughly between -3 and -4. And now the cooling fans come one and stay on in low speed when the engine is cold. Maybe a temp sensor issue?

 

[HotZ28]

A bad coil can cause spark plug contamination & failure due to lack of fire. Have you looked @ the plugs on #3 & 6?
When the A/C is set in auto climate control & set to auto, the fan(s) will also turn on if any interior cooling is needed to meet the set-point. In that case, it don't matter what the engine temp is?

 

[markfothebeast]

A bad coil can cause spark plug contamination & failure due to lack of fire. Have you looked @ the plugs on #3 & 6?
When the A/C is set in auto climate control & set to auto, the fan(s) will also turn on if any interior cooling is needed to meet the set-point. In that case, it don't matter what the engine temp is?

I have not looked at the plugs lately. They are new and have maybe 1.5 hours of just idle time. I will pull them and inspect. And the fans were running on low speed without A/C on. Oddly, the fans did not come back on again.

One thing I did notice in the Torque live data logs is that the misfiring occurs as the RPMs drop back to idle after revving the engine. According to the upstream o2 sensor, it is running lean when I let off the accelerator and in a brief moment as it settles back down the fuel trim drops between -3 and -4.

But I will definitely look at the plugs.

 

[markfothebeast]

I washed the car last night with a garden hose sprayer and it went back to misfiring like crazy again. I also sprayed the bottom of the engine to clean the massive amount oil residue off.

Perhaps there's a loose wire somewhere or a sensor that is being exposed to moisture? Can the crankshaft position sensor cause issues if it's wet or contaminated with oil residue?

 

[markfothebeast]

I'd read some horror stories about the metal spark plug boot covers causing a random misfire. I forgot to put 4 of the 6 back on. I'm going to remove the two from the rear spark plugs and see if that's the issue. Perhaps the aftermarket plug wires are arcing on these?

 

[02LTD]

I'd read some horror stories about the metal spark plug boot covers causing a random misfire. I forgot to put 4 of the 6 back on. I'm going to remove the two from the rear spark plugs and see if that's the issue. Perhaps the aftermarket plug wires are arcing on these?

Never saw arcing due to the metal boot covers. I have seen arcing due to cracked porcelain on the spark plug itself.

 

[HotZ28]

Perhaps the aftermarket plug wires are arcing on these?

What brand of "aftermarket plug wires" were installed? All plug wires are not created equal! When you do a scan, what cylinders are misfiring? Is it the ones with the shields on the boots, or others?

 

[markfothebeast]

What brand of "aftermarket plug wires" were installed? All plug wires are not created equal! When you do a scan, what cylinders are misfiring? Is it the ones with the shields on the boots, or others?

The only cylinders not misfiring are 2 and 5. The misfire is minimal on each cylinder but happens most on #6. I'm going to pull the (new) plugs and clean them. They may have fouled after numerous issues of running rich.

 

[02LTD]

The only cylinders not misfiring are 2 and 5. The misfire is minimal on each cylinder but happens most on #6. I'm going to pull the (new) plugs and clean them. They may have fouled after numerous issues of running

Have you changed ALL of the coils yet and if so, what brand?

 

[HotZ28]

In addition, What brand of "aftermarket plug wires" were installed? All plug wires are not created equal!

 

[markfothebeast]

Have you changed ALL of the coils yet and if so, what brand?

I have a bunch of OEM junkyard ones I've swapped between with the same results. I managed to rig up my broken fuel pressure gauge and it idles at 46PSI. I need to have a helper rev up the engine to see if it does something goofy.

 

[02LTD]

I need to have a helper rev up the engine to see if it does something goofy.

Why do you need a helper?
You can operate the throttle by hand.

 

[markfothebeast]

Why do you need a helper?
You can operate the throttle by hand.

Yeah. I'm dumb. I didn't think about that at the time it was so stinkin' hot outside. I'm still stumped. The fuel pressure seems okay. It isn't leaking down right away an holds at about 50PSI. The injector pulse width is at about 16ms at start up (one one bank according to Torque) and about 14ms on the other. It takes awhile for the pulse width to drop to to 3ms. It's still got a stumble at idle. Perhaps a vacuum leak? But the fuel could have water in it yet.

 

[markfothebeast]

Well, it was just faulty ignition coils. 3 out of 6 used coils in the mix were faulty... It must be a common issue.

 

[02LTD]

I’m glad you got the right mix of coils. I stopped dicking around with used coils years ago. I put 3 brand new Blue Streaks on and haven’t looked back. 😎