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

**URL:** <https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975>\
**Category:** Maintenance/Repairs\
**Tags:** escort, ford\
**Created:** [April 23, 2011, 2:15pm UTC](https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975 "2011-04-23T14:15:05Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Meg\_Duggan](https://avatars.discourse-cdn.com/v4/letter/m/9f8e36/32.png) [@Meg\_Duggan](https://community.cartalk.com/u/Meg_Duggan)\
**Post date:** [April 23, 2011, 2:15pm UTC](https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975/1 "2011-04-23T14:15:05Z")

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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?

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**Author:** ![Meg\_Duggan](https://avatars.discourse-cdn.com/v4/letter/m/9f8e36/32.png) [@Meg\_Duggan](https://community.cartalk.com/u/Meg_Duggan)\
**Post date:** [April 23, 2011, 2:19pm UTC](https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975/2 "2011-04-23T14:19:39Z")

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

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**Author:** ![Meg\_Duggan](https://avatars.discourse-cdn.com/v4/letter/m/9f8e36/32.png) [@Meg\_Duggan](https://community.cartalk.com/u/Meg_Duggan)\
**Post date:** [April 23, 2011, 2:24pm UTC](https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975/3 "2011-04-23T14:24:13Z")

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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.

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**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\
**Post date:** [April 23, 2011, 2:48pm UTC](https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975/4 "2011-04-23T14:48:09Z")

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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…

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<div class="post-metadata">

**Author:** ![Meg\_Duggan](https://avatars.discourse-cdn.com/v4/letter/m/9f8e36/32.png) [@Meg\_Duggan](https://community.cartalk.com/u/Meg_Duggan)\
**Post date:** [April 23, 2011, 5:24pm UTC](https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975/5 "2011-04-23T17:24:16Z")

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> .\< 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.

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**Author:** ![fordx4](https://avatars.discourse-cdn.com/v4/letter/f/a183cd/32.png) [@fordx4](https://community.cartalk.com/u/fordx4)\
**Post date:** [April 23, 2011, 8:44pm UTC](https://community.cartalk.com/t/1999-ford-escort-zx2-2-0-dohc-rough-idle-drop-in-rpm-when-heat-on/63975/6 "2011-04-23T20:44:17Z")

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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.