Idle adjustment question, Idles high or slowly stalls Options

[BillC]

I have an idle adjustment question for all you D-Jet gurus:

I can adjust the idle air screw on the throttle body so the car idles at 1600 RPM, and it will happily idle at 1600 all day long. If I turn in the screw just a little bit, like 1/4 turn, the car will slowly drop idle speed down slower and slower until it stalls. I can blip the throttle to keep it running, but it just wants to slow down and stall. This is all when the car is fully warmed up.

How do I get the car to idle steady around 1000-1200 RPM? 1600 is just too high.

Car is a '73 2.0 with factory D-Jet. I installed new Standard Products FJ67 injectors, and the fuel pressure is 29 psi. There are no leaks in the intake side, and the idle adjustment screw is about 2 turns out (so there's plenty of adjustment available in both directions). The MPS hasn't been messed with, and the ECU looks like the correct unit. All new vacuum lines, fuel lines, pump & filter, and fresh gas. New @JeffBowlsby engine and alternator wiring harnesses.

Known issues: it has the wrong CHT sensor (it's the one that's commonly available) and I think the TPS board has worn traces. I finally found the right CHT and ballast resistor, and I also have a 914Rubber replacement TPS board, and I will install both of them when I get a chance. However, I don't think either of those should keep it from idling at a reasonable RPM.

[emerygt350]

Have you tried playing with your timing while you are at it? I would be interested to know if retarding the timing a hair would bring it down. Remember these cars had a vacuum retard at idle of almost 10 degrees.

Did you try plugging the hole for the idle screw inside the TB venturi with your thumb? Sometimes those leak as well. Screw will be full in but it will still draw air through there.

[BillC]

Have you tried playing with your timing while you are at it? I would be interested to know if retarding the timing a hair would bring it down. Remember these cars had a vacuum retard at idle of almost 10 degrees.

Did you try plugging the hole for the idle screw inside the TB venturi with your thumb? Sometimes those leak as well. Screw will be full in but it will still draw air through there.

I did check the timing at idle while I was playing with the MPS, but it was idling at about 25 degrees advanced. Which makes sense since the vacuum in the intake was so low.

I realized later that I could have rigged up vacuum hoses and tees, to put 17" of vacuum on the distributor and the MPS simultaneously, but I'll wait for the "new" throttle body before I worry about that.

[emerygt350]

Have you tried playing with your timing while you are at it? I would be interested to know if retarding the timing a hair would bring it down. Remember these cars had a vacuum retard at idle of almost 10 degrees.

Did you try plugging the hole for the idle screw inside the TB venturi with your thumb? Sometimes those leak as well. Screw will be full in but it will still draw air through there.

I did check the timing at idle while I was playing with the MPS, but it was idling at about 25 degrees advanced. Which makes sense since the vacuum in the intake was so low.

I realized later that I could have rigged up vacuum hoses and tees, to put 17" of vacuum on the distributor and the MPS simultaneously, but I'll wait for the "new" throttle body before I worry about that.

Wait a sec here... Your timing should be 7 or 8 at idle. 25 would easily put you at the high idles you are having.

Vacuum should be doing nothing but running your mps at this point. Do you have a Bluetooth 123 dizzy? Again it's been such a long thread I can't remember your exact setup anymore.

[JamesM]

Have you tried playing with your timing while you are at it? I would be interested to know if retarding the timing a hair would bring it down. Remember these cars had a vacuum retard at idle of almost 10 degrees.

Did you try plugging the hole for the idle screw inside the TB venturi with your thumb? Sometimes those leak as well. Screw will be full in but it will still draw air through there.

I did check the timing at idle while I was playing with the MPS, but it was idling at about 25 degrees advanced. Which makes sense since the vacuum in the intake was so low.

I realized later that I could have rigged up vacuum hoses and tees, to put 17" of vacuum on the distributor and the MPS simultaneously, but I'll wait for the "new" throttle body before I worry about that.

Wait a sec here... Your timing should be 7 or 8 at idle. 25 would easily put you at the high idles you are having.

Vacuum should be doing nothing but running your mps at this point. Do you have a Bluetooth 123 dizzy? Again it's been such a long thread I can't remember your exact setup anymore.

(IMG:style_emoticons/default/agree.gif)

Something is up with your timing.

Assuming 123 sent you the correct distributor, curve "A" for the 914 has 22 degrees mechanical advance that starts ramping up at 1000 RPM, so below 1000rpm with no vacuum retard present you should be sitting at 5 deg static timing. Even with a few extra degrees advance thrown in for "idling" over 1000RPM you should be seeing a lot closer to 10 than 25

The 2.0 d-jet motors do require vacuum retard to pull the timing at idle to keep the idle speed down but it pulls a max of 10 degrees and usually gets in the ballpark of a few degrees of 0 either way.

With no vacuum line hooked up timing should be 27 deg BTDC >3000RPM
no vacuum line @1000rpm should then be ~ 5 deg BTDC
Vacuum attached @1000rpm should be anywhere from 5 deg ATDC to 5deg BTDC depending on the vacuum you are seeing.

what RPM were you seeing 25 deg advance at? You should not be seeing that until ~2500 RPM regardless of what your engine vacuum is doing.


Apologies for not seeing all this sooner, pretty busy atm and havent been checking the board much.