I have recently rebuilt the entire upper half of the engine. I'm finally moving about the city. Unfortunately, when I come to a stop, the idle drops so much that the engine quits.

Everything is basically brand new:
Fuel pump;
Fuel filter;
Fuel temperature sensor;
Fuel pressure relief;
Fuel injectors;
Fuel modulator;
Throttle position sensor;
Mass airflow sensor;
Spark plugs;
Spark plug wires;

There's nothing remaining to buy new.

My first thought is the cable for the idle itself is not positioned properly, or tightened to where it should be. Rave does not actually tell me a concise measurement on this. Anyone have any ideas on the idle level itself, where it should be, or something outside of what I have already mentioned?
At idle, when warm and the vehicle is just sitting and idling for a period, RPM is approximately 600.

 

For my '96 GEMS 4.0L Idle Speed (all loads off, i.e. lights off, A/C off, not pressing the brake, not turning the steering, shift to neutral or park) is specified 700 rpm +/- 20, ECM controlled, per the Land Rover Workshop Manual. The manual also says there is no adjustment for Base Idle, but it can be checked using TestBook. The throttle cable is tightened to remove all slack, then backed off 1/4 turn. The throttle plate should be exactly perpendicular, that is same exact measurements to top and bottom of the plate from the inlet bore, there is a screw to adjust this.

1. There is an air bypass screw under an aluminum cap just above the IACV. It sounds like your IACV is not working well, but backing this screw (allen head) out might solve your problem. Access by drilling a small hole in the cap and popping it off with a screw or such. I think factory setting is to get the IACV between 25 to 50% or so (50 to 100 steps). The engine should be able to run around 525 - 550 rpm even if the IACV path is closed (0%) because of the air allowed by the bypass screw.
2. Did you Reset Adaptive Values? I use the GEMS Lite app to do this with a generic OBD unit and a Samsung tablet. Resetting Adaptive Values is needed whenever the TPS is moved, or if other adjustments are made.
3. Tightening the throttle cable might hold the RPMs up, but that would also indicate the IACV is not working properly.
4. Maybe try unplugging the MAF to see how it runs. With the MAF unplugged, the ECM uses pre-programmed values based on throttle position and other factors.

A couple more questions to help clarify: Is the Fuel Pressure Relief the same as the Fuel Pressure Regulator? That is the unit at the end of the fuel rail with a vacuum tube attached. The vacuum tube is used to reduce fuel pressure when there is high manifold vacuum. Make sure all the vacuum lines and PCV hoses are tight. What is the Fuel Modulator? What kind of injectors did you install? Are the injectors rated 19#/hr? What is the diameter of the alternator pulley? Since the alternator feeds the rpm signal to the tachometer, it needs to be the correct diameter to get the correct rpm reading. Are the O2 sensors responding in their normal cycling patterns?

OK. I have said too much. I would start by resetting adaptive values and go from there. Good luck!

 

This community is great.

 

This could be an IACV issue or a PCV clog so you'll likely need to try a couple of things to narrow it down. Start with the cheapest stuff and move up the ladder progressively.

Clean the PVC thingy on the passenger side valve cover. Pull the hose, gently pull the plastic piece out. Be sure not to let it crack into multiple pieces. Clean and replace. The hose itself may also need replacement. They become soft and collapse.

A simple OBD reader will be very helpful.

https://landroverforums.com/forum/di...02/#post581013



and an ECU re-flash might also be one of the earliest steps (no cost). This was developed by forum member "robertf"

https://www.fixmyrover.com/


after that, if a new IACV is the call...
https://landroverforums.com/forum/di...75/#post585891

I'm inclined to bet on an IACV failure. Not terribly expensive to try.

finallly, all the workshop manuals and documentation can be found in the google drive linked in my signature. Help yourself to whatever you like.

 

First, thanks for all of these responses. Great info.

The IACV is brand new and all of the breather hoses. Walt, what does the PCV stand for? My coffee has yet to kick in.

For the record, I have a 1998, so some things are slightly different than the 1996, but not much.

Zero codes on the OBD II.

What is occurring is that when I come to a stop, my RPMs will drop, as would be normal in all vehicles. However, my RPMs just keep dropping, sometimes sputtering back upward, sometimes I can rev the engine back up. But, usually, the RPMs just drop down to zero and I have to fire it back up.

I also wonder on octane in the fuel tank. But, this should not be the case.

 

There are two time periods when electronic or electrical components are more likely to fail: Early in life (infant mortality) and late in life (old age). Plotted out, this trend is shaped like a bathtub, the famous bathtub curve. Once past the initial infant stage, reliability increases greatly. Point is, just because something is new doesn't mean it is good.

Maybe try the old IACV and see how it goes. Definitely reset adaptive values (only takes a minute once you have the tools) and monitor O2 trends.

 

PCV is 'positive crankcase ventilation'. That tube which sticks out of the passenger side of the plenum with the other end attached to the passenger valve cover. There is a little squiggly thingy in valve cover. Basically it is an oil catch. It can become clogged.

I still think it is an IACV. Perhaps it is not calibrated properly. Some have reported that an ECU reset can help in this regard. Essentially the starting position of the pintle, which moves in/out, is not known by the ECU and it only counts the positions changes.

Other than that it might be a fuel filter, fuel pump, or fuel pressure regulator.

 

Thanks for the photo, @WaltNYC - I actually do not have that on my vehicle. At one point, I had wondered on that after seeing it in RAVE when I was rebuilding. The hose, which is brand new, goes straight from the plenum to the top of the valve cover. There is a 1996 Disco in the junkyard right now, and on Sunday I can head down there and grab the one from there, then test it on mine. I can order one and have it delivered sometime next week if this is the issue.

I drove around a bit last night. When I have this thing just started, the idle stays higher and there are no issues. But, once it warms up, then the drama of the idle drop happens. At one point, the idle was dropping, and then it surged back upward to normal as if something was stuck. It made me think that there is something stuck open/closed, or any other mechanical method where the flow was not where it should be, for whatever it is that should be flowing properly.

I will head down to the junkyard on Sunday. Thanks for the continued responses.

 

Still waiting to hear your new injector specs. Maybe grab the IACV at the yard while you are there.

The description of operation sounds like the IACV is working at start, but closing down too much as the engine warms up. It is normal to start at a higher idle, then reduce as the engine warms up. I would check the bypass passage and screw for blockage. Maybe could be some interaction with the new injectors at minimun duty cycles.

Don't know if you are able to reset adaptive values, response has been eerily silent. Since the TPS was replaced, resetting is important to do. Most adaptive values adapt to operating conditions over time, but the TPS idle position is set only once using the OBD port with a scanner running the reset software, whenever the TPS is moved. If the TPS was rotated slightly CW (lower ohms than baseline), it might have an effect like you are having. If the TPS was rotated slightly CCW (higher ohms than baseline), then the engine can start at very high RPMs (nearly 2250) and stay there until shifted into gear. So resetting is important in your case. Let us know what your thoughts are about this.

 

So if you are telling me there may be a hot/cold element I would introduce the idea that your crank sensor may be failing. They are notoriously heat sensitive when they start to fail. One approach to diagnosing a failing ckps is to pour cold water on it once it is hot and stumbling or outright dies. I've seen accounts of a truck dying when it gets to operating temp and not starting again until it cools down. A good dowsing of cold water on the ckps has been know to temporarily solve the no start problem.

IACV and fuel pump remain in play.