85 3.8 C5 auto, rpms drop when in gear

[PittsPeng]

1985 3.8 with a C5 auto trans. When I’m in park or neutral, it’ll idle at 650-700~. But as soon as I put it in drive or reverse, the rpms drop to 375-450~.

Any suggestions on what to test?

 

[CarMichael Angelo]

Why is this not normal?

Every auto trans car experiences a rpm drop in drive Vs park/nuetral.
Is this the first car you've ever been in?

 

[Deleted member 215073]

Shouldn't an automatic equipped car have a higher idle than 750?

 

[General karthief]

What rpm does it idle at and how much does it drop when you put it in gear
never mind!
Does it stall or stumble? I'd be suspicious of the factory tach, I can't see it actually idling that low but what do I know

 

[PittsPeng]

It does stumble and idle really rough when placed into gear (cold or at operating temp).

And to CarMichael Angelo, it is the first auto that I’ve ever had such a significant rpm drop when placed into gear. Then again, only autos I’ve ever owned were a 95 Grand Prix and currently a 17 Fusion 2.0EcoBoost AWD. Everything else has been a manual transmission.

 

[PittsPeng]

Shouldn't an automatic equipped car have a higher idle than 750?

The idle and emissions sticker is missing, so idk what the factory idle is supposed to be at. I literally just got the car a couple weeks back and have less than 50 miles on it since I acquired it. I’m doing a full tune up this week just in case.

 

[PittsPeng]

UPDATE:

So I live in the country. Today, while in town for the first time, it stalled after sitting in gear at a light. But I’m fine when I put it in neutral/Park while at a light.