93 Eurovan - Accelerator pedal/stalling issues

Question

Recently picked up a '93 Eurovan Automatic. It has had a couple of issues since I've owned it. Currently driving across the US after being told the van was mechanically alright.

There are a couple of issues at the moment.

1. On startup the motor revs up just fine, gets to around 1400rpm as expected and drops from there. Sometimes it manages to keep running after a little inconsistent idling, most of the time it just drops straight back down and stalls. Gentle pressure on the accelerator for a few seconds (~1500 - 2000rpm) while in park will keep it running through this initial instability and then from there it's fine idling. Having the hood of the car popped seems to help a little with this issue too - airflow/vacuum?

2. After the car is started and idling fine, upon gentle pressure on the accelerator while in D or R the car will sometimes stall. As soon as the rpms are a little higher and the car is running it's fine. Doesn't stall once you're above 1000rpm in 1st gear. This issue is usually less severe when the engine is warmed up.

3. The accelerator pedal will completely stop responding while driving at highway speeds in warm weather. Pressing the pedal won't affect the rpms or speed at all. After pulling over and waiting for some time the car will be able to drive again. After a short time the same issue will occur. This has only ever been an issue in hot weather. Presumably waiting for the car to cool down temporarily fixes the issue then upon heating up again the accelerator cuts again?

Issue 3 has occurred before. Just after buying the van we had the same issue. 2 separate mechanics have told us it was the coolant temperature sensor allowing the van to overheat. Both mechanics replaced the sensor and a coolant flush/replacement was done too. The van does get quite hot while driving but we have never had the temperature warning light come on (lights up briefly after turning key to on position, never seen it lit outside of this). The temperature gauge doesn't work (neither does the fuel gauge), it sits at 1/4 most of the time (when the fuel gauge sits at empty) and then sometimes rises up to near max. I was told this isn't an issue. Is the temperature warning light connected to the dash gauge? The spark plugs and wires as well as the fuel and air filters have also been replaced recently.

Any help at all would be appreciated tons, especially as mechanics have failed to diagnose the issue and money has been spent.

Thank you!

Answer 1

Ok, you’ve got a few (very well written) questions, so I will try to answer the ones which I am able to.

Stalling

Based on the fact that the stalling is prevented/reduced by pressing the accelerator or by opening the hood, it sounds like the engine may not be getting enough air.

(New addition to my answer below)

Regarding the accelerator pedal stopping working: I have a '92 Ford Ranger which would experience a similar problem. Driving along, the gas pedal would "stop working", and the RPMs would drop to the idle rate. It was as if someone cut the throttle cable. It would typically last for less than 30 seconds. It turned out being a problem with my MAF (Mass Air Flow) sensor. The MAF would intermittently stop working, and the engine would think that the throttle was closed (because the MAF was not sensing any airflow). Unplugging the MAF fixed the problem.

If you unplug the MAF, the check engine light will probably turn on, and your gas mileage may drop slightly. This is because the engine switches to a "default fuel mixture", which is typically slightly richer than necessary.

Overheating

Did the mechanics specifically say they replaced the coolant temperature sensor? In your case, I do not think this is causing any problems with overheating.

The coolant temp sensor is an electrical thermometer that sends temp readings to the gauge on the dashboard, and in some cases to the car’s computer.

If you look at page 9 of the wiring diagram below, it looks to me like the engine coolant temp sensor is connected to the coolant temp gauge (instr clstr). I marked both in yellow.

I noted (using green lines) that both the wire coming from the engine coolant temp sensor and the wire going to the coolant temp gauge are YEL-RED (meaning yellow with a red stripe), so I am fairly confident that that the coolant temp sensor only is used by the temp gauge on your dashboard. As a result, I do not think the coolant temp sensor is causing the engine to overheat.

Note: You can see I also put blue boxes around the different parts of the afterrun coolant pump. This is a pump which cools the engine's turbo after the car has been shutdown. It is an electrical pump, whereas the primary coolant pump is mechanical. If your engine has a turbo, the afterrun coolant pump cannot cause the engine to overheat.

In your case, I think the mechanics should have checked the thermostat. It is a mechanical device which opens and allows coolant to flow from the engine to the radiator when the coolant gets hot. In many cases when engines are overheating, it is simply because the thermostat is stuck in the closed position, and is not allowing coolant out of the engine into the radiator.

It is fairly easy to check if the thermostat is working. When the engine is fully warmed up, feel the hose which connects to the top of your radiator. It should feel very hot, because it is carrying the hot coolant out of the engine. If you squeeze it, it should feel like it is full of coolant. If it feels empty, that means that only a small volume of coolant is leaving the engine.