As posted by @involuted:
Here’s everything I’ve learned from troubleshooting throttle valve problems on my Series 2 diesel van!
This system isn’t covered in my workshop manual, and my mechanic hadn’t seen it before since Series 2s are still rare in the USA. There’s some good info on the Australian Delica Club forum, but it’s fragmented and incomplete (and sometimes wrong). I'm hoping this can be a complete reference.
This applies only to 4M40 (diesel) Series 2 L400s made before mid-1999. Series 1 vans do not have this system. Apparently 1999+ vans only have one throttle valve - see here and here.
It’s unclear why this system exists. People speculate that it marginally improves efficiency or emissions. However, the van still runs just fine if you disable it. Disabling it takes 30sec and requires no parts/tools.
When this system fails, it starves the engine of air. This can cause either stuttering and pinging when idling or power loss when driving, plus lots of acrid grey/black smoke (poorly combusted diesel). If this happens to your Series 2 van, check the throttle valve system before you start rebuilding your injectors, pump, etc - you might save a lot of money and time.
The external portion of the two valves look like flying saucers with levers coming off the bottom. The valves are vacuum-actuated and controlled by solenoids:
The solenoids control whether the valves are under vacuum. When under vacuum, the valve levers lift up; otherwise they stay down. (Up/down does not necessarily mean open/closed! This will be discussed later.)
Note that the valve levers are mirrored around the vertical axis. The shutdown valve lever rotates clockwise from 8:00 to 10:00 when opening, and the idle valve lever rotates counterclockwise from 4:00 to 2:00.
Internal components
The internal portion of each valve is a butterfly (flap) that opens and closes an air hole in the throttle body. The idle adjust hole is large and the shutdown assist hole is small:
For some reason the two valve levers move the butterflies in opposite ways. When the idle adjust lever is down, its butterfly is closed. When the shutdown assist lever is down, its butterfly is open. You can see in the bottom-view photo below that both levers are down, but the butterflies are in opposite states:
And here's a table of all the normal behaviors:
Next, check your van’s throttle valve behavior against the table of normal behaviors above. If any of the lever positions don’t match the table at the time the van is misbehaving, you've probably found your problem.
I’ve seen two different problems in my van:
Check vacuum tube connections
Make sure they match the pictures earlier in the article. People (including me) have been known to connect the wrong tubes to the wrong valves!
Check vacuum system has vacuum
Disconnect an input line and then cover it with your finger. You should be able to feel suction when the van is running. (If you don’t have any vacuum, it will probably cause other problems as well - eg I’ve read it will interfere with shifting into 4wd - but I haven’t seen that myself.)
Bypass solenoids to hold valve in a constant state
When you bypass a valve, your goal is to keep its butterfly open all the time so that engine airflow is never restricted. This does not have any visible negative effects. Some Delica shops even do this on every van they see!
To bypass the idle adjust valve, connect it directly to the vacuum input, bypassing the solenoid. That will keep the butterfly always open (lever always up). Here's a picture of that:
I never actually tried to bypass my shutdown assist valve alone, but in theory you could disconnect it from all inputs to keep the butterfly always open (lever always down). Make sure the vacuum input that used to be going into it is plugged so you don't create a vacuum leak.
To bypass both valves, you could try doing both of the things listed above. Or, to make things simpler, connect both valves directly to vacuum. In that case, the big butterfly is always open and the small butterfly is always closed. I tested this and it also seems to work fine.
Replace solenoid
You can try to order a replacement solenoid. I successfully used a K5T43992 which I got on Ebay for ~$35 with free shipping to the USA.
Alternatively, if you have an EGR delete, you can swap in one of the supposedly-identical EGR solenoids. Deleted EGR solenoids are usually left in place but with the vacuum lines disconnected (supposedly it can trigger error codes if you fully remove them). My van does have EGR deleted, but I never tried re-using those solenoids.
Before doing this, it’s a good idea to:
Adjust butterfly screw
If bypassing/replacing the solenoid does not help, perhaps your butterfly is stuck or misaligned. This has never happened to me, but I’ve read that when it does happen, you can tell by feel. Try adjusting the screw on the valves near the levers to adjust the butterfly mechanisms - details here.
Here’s everything I’ve learned from troubleshooting throttle valve problems on my Series 2 diesel van!
This system isn’t covered in my workshop manual, and my mechanic hadn’t seen it before since Series 2s are still rare in the USA. There’s some good info on the Australian Delica Club forum, but it’s fragmented and incomplete (and sometimes wrong). I'm hoping this can be a complete reference.
This applies only to 4M40 (diesel) Series 2 L400s made before mid-1999. Series 1 vans do not have this system. Apparently 1999+ vans only have one throttle valve - see here and here.
Summary
The throttle body assembly (ME202203) contains two vacuum-actuated valves which are controlled by solenoids:- Idle adjust valve (front): Slightly restricts engine airflow when the engine is hot and idling
- Shutdown assist valve (rear): Greatly restricts engine airflow when the engine is shutting down
It’s unclear why this system exists. People speculate that it marginally improves efficiency or emissions. However, the van still runs just fine if you disable it. Disabling it takes 30sec and requires no parts/tools.
When this system fails, it starves the engine of air. This can cause either stuttering and pinging when idling or power loss when driving, plus lots of acrid grey/black smoke (poorly combusted diesel). If this happens to your Series 2 van, check the throttle valve system before you start rebuilding your injectors, pump, etc - you might save a lot of money and time.
How it works
External componentsThe external portion of the two valves look like flying saucers with levers coming off the bottom. The valves are vacuum-actuated and controlled by solenoids:
The solenoids control whether the valves are under vacuum. When under vacuum, the valve levers lift up; otherwise they stay down. (Up/down does not necessarily mean open/closed! This will be discussed later.)
Note that the valve levers are mirrored around the vertical axis. The shutdown valve lever rotates clockwise from 8:00 to 10:00 when opening, and the idle valve lever rotates counterclockwise from 4:00 to 2:00.
Internal components
The internal portion of each valve is a butterfly (flap) that opens and closes an air hole in the throttle body. The idle adjust hole is large and the shutdown assist hole is small:
For some reason the two valve levers move the butterflies in opposite ways. When the idle adjust lever is down, its butterfly is closed. When the shutdown assist lever is down, its butterfly is open. You can see in the bottom-view photo below that both levers are down, but the butterflies are in opposite states:
How it’s supposed to behave
I took a couple videos of the valve levers in action:And here's a table of all the normal behaviors:
| Engine states | Valve lever state | Throttle hole state | Air flow |
| Cold idle Revving Driving | Shutdown lever down Idle lever up | Both holes open | Maximum |
| Hot idle Fully off with no vacuum | Both levers down | Only small hole open | Restricted |
| Shutting off | Shutdown lever up Idle lever down | No holes open | Blocked |
| [Doesn’t normally happen] | Both levers up | Only big hole open | Slightly restricted |
Diagnosing problems
First, check your engine error codes. If you have an error code 41, one of your throttle valve solenoids is probably bad. However, a lack of error codes does not necessarily mean the system is working.Next, check your van’s throttle valve behavior against the table of normal behaviors above. If any of the lever positions don’t match the table at the time the van is misbehaving, you've probably found your problem.
I’ve seen two different problems in my van:
| Throttle valve malfunction | Symptoms | Reason |
| Idle adjust stuck closed (due to flaky solenoid) | Intermittent, when accelerating:
| The big throttle hole is always closed, so the engine can only get air through the small hole. That’s OK when idling, but it’s not enough air for higher RPMs. |
| Shutdown assist stuck closed (due to incorrect vacuum tube connections) | When idling with engine hot:
Normal when driving. Normal when idling with engine cold. | The small throttle hole is always closed. When the big throttle hole is open (cold idling, driving), this is not a problem, but when the big hole closes (hot idling), engine airflow is completely blocked. |
Troubleshooting
Check vacuum tube connections
Make sure they match the pictures earlier in the article. People (including me) have been known to connect the wrong tubes to the wrong valves!
Check vacuum system has vacuum
Disconnect an input line and then cover it with your finger. You should be able to feel suction when the van is running. (If you don’t have any vacuum, it will probably cause other problems as well - eg I’ve read it will interfere with shifting into 4wd - but I haven’t seen that myself.)
Bypass solenoids to hold valve in a constant state
When you bypass a valve, your goal is to keep its butterfly open all the time so that engine airflow is never restricted. This does not have any visible negative effects. Some Delica shops even do this on every van they see!
To bypass the idle adjust valve, connect it directly to the vacuum input, bypassing the solenoid. That will keep the butterfly always open (lever always up). Here's a picture of that:
I never actually tried to bypass my shutdown assist valve alone, but in theory you could disconnect it from all inputs to keep the butterfly always open (lever always down). Make sure the vacuum input that used to be going into it is plugged so you don't create a vacuum leak.
To bypass both valves, you could try doing both of the things listed above. Or, to make things simpler, connect both valves directly to vacuum. In that case, the big butterfly is always open and the small butterfly is always closed. I tested this and it also seems to work fine.
Replace solenoid
You can try to order a replacement solenoid. I successfully used a K5T43992 which I got on Ebay for ~$35 with free shipping to the USA.
Alternatively, if you have an EGR delete, you can swap in one of the supposedly-identical EGR solenoids. Deleted EGR solenoids are usually left in place but with the vacuum lines disconnected (supposedly it can trigger error codes if you fully remove them). My van does have EGR deleted, but I never tried re-using those solenoids.
Before doing this, it’s a good idea to:
- Confirm that bypassing the solenoid fixes the issue!
- Test the resistance of the solenoid to confirm it’s actually bad (vs getting bad instructions from the ECU or something). The workshop manual says the EGR solenoids should read between 36-44 ohms - it doesn’t address the throttle valve solenoids but I’ve read they are the same. IIRC when I had a broken solenoid the resistance was very high.
Adjust butterfly screw
If bypassing/replacing the solenoid does not help, perhaps your butterfly is stuck or misaligned. This has never happened to me, but I’ve read that when it does happen, you can tell by feel. Try adjusting the screw on the valves near the levers to adjust the butterfly mechanisms - details here.