What bothered me most was that it was running fine, then it started only once in a while, then at every startup. It's gonna be fun at -30 this winter.

I also noticed that if I lift off the throttle all at once it will die because revs drop too low.

Codes have been checked and rechecked. No codes or pending codes. All wiring is accounted for. Voltage output was tested while running, we backprobed the connectors. No fuel leak, fuel pressure was tested again, 38-39 PSI at startup. I also replaced a couple vacum hoses.

 

Exactly the same thing happened to mine. I attributed it to still having the original IACV now with 160k on it. It and it's ports are so clean you can eat off them. When I took the Base Idle screw out completely it's port and needle tip had allot of carbon so I cleaned them and two ports in the plenum. In my case I think a new IACV is in the future plus having the base idle and ECM reset.

I've been looking for a diagnostic system on the cheap that can do the resets.

 

Maybe for the short term you can put in a hack to keep the throttle open a bit
like a lawn mower carb that has an adjustment screw...

This problem you are describing will take some time to resolve it looks like as you need Rover specific test book routines run against your ECU.

 

I had some trouble on my last drive. After a while the truck started to hesitate as soon as I gave it throttle, but was idling fine, per the previously made adjustment.

It started slowly then became really worse, I wasn't able to go past 20 kph. When in park I wasn't able to rev it. Even if I gave it throttle slowly it woudn't go higher than 2500 rpm. No CEL, didn't have acces to a code reader to get the live data feed.

My first guess was lack of fuel/fuel pump going out, but it was backfiring when given too much throttle. Shutting it down then restarting it (starts fine) clears the issue for an undetermined period of time. It must be a faulty sensor somewhere, my toughts are on the vss, but I can't verify it as long as I don't use a code reader.

 

Disconnect the VSS and see how it runs.

 

I would swap the ECU.
If you can get one cheap, why not?
But then will the new ECU need to be married to the BCeM?

Replacing the ECU may cause the truck to immobilize.

Mike and Savannah will know this answer spot on.

 

D1 does not have a BCem or a BCU, but has an alarm module that sometimes needs link up. I was lucky, mine did not.

 

Here is some more ideas from the web on forcing the ECU to recognize the IACV:

Fully open is 0 steps, fully closed is 180 steps. IIRC base idle is 88 steps. A scanner is not needed. In most cases the ECU will adapt very quickly. If it doesn't it's a simple matter of teaching it by the following procedure.

Key on, plug in IAC
Key off unplug IAC
key on, plug in IAC
Start engine and run at 2000rpm for 30 seconds.

You have to wait until you hear the relay drop out between steps since the IAC position with the ignition off is fully closed (180 steps).

 

I'd check vacuum and compression on the cylinders. I would almost bet you have issues with both tests

 

It was something I wanted to look into if the test on the VSS is inconclusive. But When I replaced the ECU I also replaced the alarm box with the matching unit. I still have my other ECU which I know is in good working order. I never had any problems with the ECU not matching with the alarm box as long as you don't arm the alarm system.

My other option besides the VSS and the ECU is the alarm spider.

Savannah, I tried that procedure several times without any success.

ArmyRover, when I shut it off, it cleared the issue. This makes me think it should be an electronics issue rather than mechanical.