Engine idles low, when in gear the idle is so lower

Good evening folks,

I've got a stupid question:

My 35th is acting kind of strange, I bought this as a project car and it seems it really is one... The car is idling very low, around 600-700 RPM in nutral. It is an auto, when I put it in Rev or D it drops to around 500RPM, as long as I keep the idle up to around 800RPM it stays pretty smooth and runs well. Tonight I noticed that while in gear, AC on the idle was dropping so low that the oil pressure gauge would fall off to nothing and make the Check gauges like come on in the instrument cluster. As soon as I brought the idle back up to around 800-850 oil pressue is way up there and the idle is smooth... This car has seen much better days and I'm rebuilding things as I find them, it's not on the road yet so I can't tell what it really does on the open road. Speedo was out also when I drove it home.. The head gaskets appear to have been done. I thought maybe an intake leak somewhere, but tonight I did the old Carb Cleaner thing on it and I didn't find any vacum leaks... Anyone got any ideas??

Two words, ....motor mounts. My 35th did the low idle thing from the day I owned it. After seeing so many posts about how bad mounts would allow the engine to settle and cause crimped power steering lines and low idle, I figured because of it's mileage I would go ahead and change them. When I picked the car up, I couldn't tell it was running. Upon driving it home, I kept having to check the tach to make sure it was still running because the idle was so smooth. I won't say that plugs and other components can't be the problem but motor mounts was an eye opener for me. Just a suggestion.

My best to you and good luck.

Hey Lance,

That was the first thing I looked at, this weekend when I had it up for that brake pressure sensor. I looked pretty closely at them... The don't look like they've been there very long. Might have gotten done when the heads GSKTs were replaced... Looks like maybe a real shop did all the work before this kid got it..

What is it exactly that controls the idle on these things?? I saw an idle or butterfly stop screw on the throttle body but thought the idle was controlled electronically... Hence my thought process on the speedo being out and the wierd oil pressure readings... I was thinking it was something electronic..

I know it needs new plugs wires and possibly plugs too... To many parts to change not enough hours in the day after work!!! I also played with my lousy little code reader... KOEO test was showing two codes an 18 and a 29...

Let's see, and it's hard to start too, seems to turn over quite a bit before it starts...

Well, 18 is a grounded spout connector and 29 is poor voltage from the vehicle speed sensor. As far as what controls idle, the bottom line is the computer. The various sensors give the computer it's variables and then it decides what to do. I think what I would do since this is an unfamiliar vehicle is tediously check all of the electical connectors and make sure all of them are clean and not exposed or crimped in some way. And fuel pressure can be a culprit if the pump(s) are weak or have a clogged filter. These are just the first things to come to mind, Richard. Wish I could be better help.

One thing I keep forgetting is to use fuel injector cleaner in these newer cars. It never fails to improve things when I do. Just to used to the older Boss cars. I'll get there though.

Good luck and keep in touch.