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.

[JeffBowlsby]

Im no guru, but the air screw is doing what its supposed to. 1/4 turn on it (90 degrees?) is actually quite a bit and sounds excessive.

1. Try turning the air screw much less, say 20 degrees at time to reduce the idle rpm, but not shut the engine down.

2. Idle mixture is set by the ECU knob which adjusts the ECU. For that knob to function, two contacts in the TPS need to be in contact to signal the ECU to take control of idle functions. All to say, confirm that your TPS is functional for all 4 circuits and that the TPS is calibrated correctly which will signal the ECU to control idle.

3. Check for other free air leakage locations, this can get tough - be thorough until you find a leak if it exists. AAR closed when warm? Injector gaskets well seated and not causing an air leak? Use a smoke pencil on the intake plumbing to check for free air making its way around gaskets, the TB pivot bushings, the air plenum etc.

Hopefully this solves it.

[BillC]

Im no guru, but the air screw is doing what its supposed to. 1/4 turn on it (90 degrees?) is actually quite a bit and sounds excessive.

1. Try turning the air screw much less, say 20 degrees at time to reduce the idle rpm, but not shut the engine down.

2. Idle mixture is set by the ECU knob which adjusts the ECU. For that knob to function, two contacts in the TPS need to be in contact to signal the ECU to take control of idle functions. All to say, confirm that your TPS is functional for all 4 circuits and that the TPS is calibrated correctly which will signal the ECU to control idle.

3. Check for other free air leakage locations, this can get tough - be thorough until you find a leak if it exists. AAR closed when warm? Injector gaskets well seated and not causing an air leak? Use a smoke pencil on the intake plumbing to check for free air making its way around gaskets, the TB pivot bushings, the air plenum etc.

Hopefully this solves it.

I've already done the leak checking with a smoke machine (mentioned in the un-DAPO thread). So, it's confirmed there are no undesired leaks in the intake system. Also made sure the AAR closes properly when warm.

I've been trying to adjust the idle air screw in small increments. Unfortunately, I can make multiple small adjustments (5-10 degrees) with no change in the idle, and then one more little tweak will cause the engine to start it's downward spiral. Once that starts, I need to back the idle screw out like 1/2 turn or more to get it back to 1600 RPM.

It's quite possible the TPS is not adjusted properly. It's one of the few things I haven't adjusted from the previous owner. My plan, when I replace the TPS board, is to just remove the whole throttle body from the car and adjust it on the bench before reinstalling.

Anyone got a link to the TPS adjustment procedure?

[Ron914]

Im no guru, but the air screw is doing what its supposed to. 1/4 turn on it (90 degrees?) is actually quite a bit and sounds excessive.

1. Try turning the air screw much less, say 20 degrees at time to reduce the idle rpm, but not shut the engine down.

2. Idle mixture is set by the ECU knob which adjusts the ECU. For that knob to function, two contacts in the TPS need to be in contact to signal the ECU to take control of idle functions. All to say, confirm that your TPS is functional for all 4 circuits and that the TPS is calibrated correctly which will signal the ECU to control idle.

3. Check for other free air leakage locations, this can get tough - be thorough until you find a leak if it exists. AAR closed when warm? Injector gaskets well seated and not causing an air leak? Use a smoke pencil on the intake plumbing to check for free air making its way around gaskets, the TB pivot bushings, the air plenum etc.

Hopefully this solves it.

I've already done the leak checking with a smoke machine (mentioned in the un-DAPO thread). So, it's confirmed there are no undesired leaks in the intake system. Also made sure the AAR closes properly when warm.

I've been trying to adjust the idle air screw in small increments. Unfortunately, I can make multiple small adjustments (5-10 degrees) with no change in the idle, and then one more little tweak will cause the engine to start it's downward spiral. Once that starts, I need to back the idle screw out like 1/2 turn or more to get it back to 1600 RPM.

It's quite possible the TPS is not adjusted properly. It's one of the few things I haven't adjusted from the previous owner. My plan, when I replace the TPS board, is to just remove the whole throttle body from the car and adjust it on the bench before reinstalling.

Anyone got a link to the TPS adjustment procedure?

Hi Bill ,
It's on the 914 Rubber TPS purchase page. Its in the installation section for the TPS