Idle drops when transmission is shifted into park

1995 DODGE CARAVAN
96,000 MILES • 3.3L • V6 • 2WD • AUTOMATIC
Avatar
RADIOFLYER256
  • MEMBER
  • 3 POSTS
I deliver newspapers with this van. Idles just fine most of the time. But while out delivering, I put the van in Park and the idle drops to about 250 RPMs according to the tachometer. Doesn't always happen, but i would say at least 70 percent of the time. Usually idles around 500 to 600 RPMs. I went to start the van yesterday afternoon, and it didn't want to stay running (was parked on a very slight decline). Work I have performed:

Spark Plugs and wires.
Oil Change.
Idle Air Control Valve.


Any thoughts on what could cause this? Perhaps a large electrical draw? I have yet to check alternator output, but the gauge on the dash shows right in the middle when running.
Feb 10, 2022 at 7:57 PM
Advertisement
Avatar
RADIOFLYER256
  • MEMBER
  • 3 POSTS
I think I need to clarify. I just re-read what I wrote. The idle dips to 250, then comes back up to 500ish. And it's not a gauge issue. The engine sound confirms.
Feb 11, 2022 at 2:26 AM
Avatar
CARADIODOC
  • CERTIFIED EXPERT
  • 34,306 POSTS
Before we went looking for the hard stuff, was the battery recently disconnected or run drained? If it was, you need to do the relearn procedure for "minimum throttle". You may never reach the requirements with stop-and-go driving at slower speeds. Drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals. If that doesn't help, do that again while holding the brake pedal up with your foot. Sometimes a slightly misadjusted brake light switch aborts the relearn.

If that doesn't help, we're going to need a scanner to see what the Engine Computer is doing and responding to. Specifically, we need to see what "idle step" it is placing the idle speed motor too. That motor is used by GM and Chrysler and has been extremely reliable. What used to cause more trouble was the air passage it controlled would become plugged with carbon. That was more common on the 3.0L engines, but due to better fuel additives, we haven't seen that for a long time. These articles describe somewhat how this system works. Your idle speed motor is of a different design, but much of the information is still of value:

https://www.2carpros.com/articles/how-a-idle-air-control-valve-works

https://www.2carpros.com/articles/idle-air-control-valve-service

https://www.2carpros.com/articles/stall-at-idle

The last article refers to stalling, but that's because of idle speed that's too low. This can also show up as a crank / no-start condition unless you hold the accelerator pedal down 1/4", and you won't get the nice "idle flare-up" to 1500 rpm at start-up.
Feb 11, 2022 at 3:10 PM
Advertisement