1999 Ford Escort Zx2 2.0 DOHC Rough Idle drop in RPM when heat on

ford
escort

#1

So I turn the heat on, and my engine feels like it’s going to stall out, the RPM’s drop by 200. What could this be?


#2

Also, It does this if the car is in neutral, or any gear, stationary or moving.


#3

Also, I did get a new water pump, and my check engine light is flashing a code for P420. Haven’t asked mechanic yet. It’s been doing this for two cold seasons now.


#4

Your car is fairly sick and you need to just take it to your mechanic.

In one of your follow ups you said that “my check engine light is flashing a code for P420” - clarify that since your check engine light won’t flash codes. It will flash, however, and if you are driving with a flashing check engine light then you risk turning what may be a simple, repairable problem into a much more expensive, perhaps car-killing problem.

As for the rpm drop, there are a couple of things. One is that the fan does put some load on the electrical system. If your battery/charging system are not healthy power draws can lead to engine stumbles. Its also likely, however, that your vent selector is set to defrost which will activate the A/C compressor. The A/C compressor puts a major load on that tiny engine.

Anyway, it doesn’t sound like you are going to be dealing with this so you just need a good mechanic. Your battery & charging system should be checked out. You should also make sure that all maintenance is current - spark plugs, wires, filters…


#5

.< I shouldn’t have said the light was flashing, it’s steady. Catalytic function below threshold. I just changed the battery and the alternator. Starter is new as well.


#6

The ZX2 has only a couple of vent position selections where the A/C compressor does NOT run. If you use the bi-level position, the A/C runs even though you haven’t turned it on. The compressor loads the engine and drops the rpm. Read your owner’s manual.