What Should Idle be at for Automatic in Park

[David T]

If your idle motor system is operating correctly it shouldn't drop at all. It may dip for a moment when the compressor clutch engages and then it should return to the original idle speed. The tach is not the most accurate indicator and it may not be reading correctly. Also remember when the clutch engages, if the cooling fans are not running then they also hit the electrical system hard and make the alternator that much harder to turn too. The whole electrical system experiences a voltage drop and the tach is sensitive to that and can read low just because of the low system voltage.
David Teitelbaum

[Bill Robertson's Sock Puppet #1]

If Charlie is idling via the brass manifold screws (B27 style) rather than CIS then his idle speed will indeed vary slightly with engine load. And as Charlie has identified, idle speed never does vary more than 100 RPM. Volvo produced thousands of A/C and automatic transmission equipped vehicles with PRV's throughout the 1970's no problem. Active idle control did not appear until 1980 -- it is a relatively late addition to the K-Jet package. (B27's did have an aux air valve that opened when the engine was cold, but it was ambient thermally operated -- no electrical connection whatsoever. That valve could not be wired to open in response to the A/C compressor or transmission).

[dmc6960]

Assuming you mean your idle speed drops 300 RPM from Park idle to Drive idle. And jumps back up when going back into Neutral or Park?

As noted in the posted manual pages and in other posts the OEM Bosch K-Jet setup compensates for all engine loads and warm-up variables to keep the idle speed within the specified range regardless.

The symptom you report makes sense - IF your EFI system does not have any idle speed modulation/control - OR if that idle speed control loop is malfunctioning. Check your EFI documentation or hardware or get input from an owner running what your are running. Am not familiar with Megasquirt - one of the posts suggests that's what you're running.

I'd guess that a modern EFI system should not run the way you are reporting yours runs. You did not mention what your idle speeds are. Does the car lurch a bit when you engage Drive or Reverse?

I dont think his particular setup uses active control. Its a stepper motor for opening and closing the idle air supply, programmed with a warmup curve, but no realtime response or adjustment. This was one of the reasons I kept the stock idle system when I went EFI. Its a very well designed and simple system. The reason for the RPM drop when in drive is the torque converter load on the engine. Its just like dragging it down with an AC compressor or higher alternator load. Without an active response system, you need sensors and programming to detect and adjust for those things like the Auto Transmission and AC Compressor. The default Megasquirt EFI does not have this.

[Bill Robertson's Sock Puppet #1]

Such a setup does work. Farrar Hudkins' carbureted PRV w/ automatic transmission similarly has a thermally activated fast idle cam with 4 stepdowns (one big one at initial startup and three smaller ones during warmup). He sets his idle speed high enough in Park to compensate for torque converter load in Drive -- an extra 200 RPM or so. This is what it looks like in action:

[lazabby]

Dave is correct. See images below taken from the Manual.

First image shows the spec. Second image shows how to test and troubleshoot.

It doesn't matter what gear the auto transmission is in. Park is fine.

Attachment 15630 Attachment 15631

What manual is this out of? Sure not the Workshop manual.

[DMC5180]

What manual is this out of? Sure not the Workshop manual.

Most likely this one: http://store.delorean.com/p-9199-manual-tech-info.aspx

[Rich]

What manual is this out of? Sure not the Workshop manual.

Confirming those images are from the original DMC Tech Info Manual as suggested by DMC5180.

It's a handy general reference vs. the more massive Workshop Manual.

[lazabby]

I dont think his particular setup uses active control. Its a stepper motor for opening and closing the idle air supply, programmed with a warmup curve, but no realtime response or adjustment. This was one of the reasons I kept the stock idle system when I went EFI. Its a very well designed and simple system. The reason for the RPM drop when in drive is the torque converter load on the engine. Its just like dragging it down with an AC compressor or higher alternator load. Without an active response system, you need sensors and programming to detect and adjust for those things like the Auto Transmission and AC Compressor. The default Megasquirt EFI does not have this.

Jim,
Have you tried the closed loop settings? This is suppose to help compensate for sudden loads on the engines. I'm trying to understand it. I found links on it but they are not very helpful.

[Jonathan]

Assuming you mean your idle speed drops 300 RPM from Park idle to Drive idle. And jumps back up when going back into Neutral or Park?
As noted in the posted manual pages and in other posts the OEM Bosch K-Jet setup compensates for all engine loads and warm-up variables to keep the idle speed within the specified range regardless.

The symptom you report makes sense - IF your EFI system does not have any idle speed modulation/control - OR if that idle speed control loop is malfunctioning. Check your EFI documentation or hardware or get input from an owner running what your are running. Am not familiar with Megasquirt - one of the posts suggests that's what you're running.

I'd guess that a modern EFI system should not run the way you are reporting yours runs. You did not mention what your idle speeds are. Does the car lurch a bit when you engage Drive or Reverse?

If this is what Shannon meant initially, my car has historically done the same thing. My car is a standard set up in terms of fuel system as well.

I can at times start the car and it may or may not idle slightly high, go for a drive and things are fine, then pull back into the garage and when I put it in park, the idle jumps a few hundred.

I've worked on a few adjustments such as what David mentioned, and some have made a noticeable change. I believe in my case it was related to the throttle linkage having too much play and it was not always returning the spool back to zero and engaging the idle microswitch.

It may be that there are a few other things at play though such as a vacuum leak somewhere too. I have never found one, but have not looked everywhere yet. If I am out driving around for the day, the car idles quite well around the 775 RPM if pulling up to a light or stop of some kind, but if after the car is plenty warmed up, it often spikes up when you finally put it in park. Not sure what the problem is exactly.

[axh174]

It may be that there are a few other things at play though such as a vacuum leak somewhere too. I have never found one, but have not looked everywhere yet. If I am out driving around for the day, the car idles quite well around the 775 RPM if pulling up to a light or stop of some kind, but if after the car is plenty warmed up, it often spikes up when you finally put it in park. Not sure what the problem is exactly.

Jonathan, it sounds like you and I are experiencing the same thing. I used to have a rock solid idle at 775 RPM when warming up and when running warm. Within the last year, I noticed that it runs at 775 RPM when warming up in both park/neutral and drive, but gets 900-1000 RPM in park/neutral and 775 RPM solid in drive once it has fully warmed up. It will spike high whenever pulled out of Drive and put into Park/Neutral after warmup.

I actually let it warm up by idling once to see what would happen, and I saw that as the car warmed up the idle RPM slowly climbed from 775 to ~950 Haven't really had the chance to dive into it tracking it down yet, though.