why when in gear idling and you turn ac on or heater on does it rough idle


Asked by Aug 19, 2014 at 04:19 PM about the 2001 Ford Escort

Question type: Maintenance & Repair

car runs fine ac on works fine but when at stop sign it runs realy rough when i use heater it also does this?

10 Answers


Sounds like your idle air valve is not compensating for extra load from AC compressor be it a control issue or a physical problem with idle air valve it self. When you say heater do you mean defrost because AC generally works on defrost to dehumidify

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when i say heater i mean no matter weather i put the heater on for heat or i put ac to cool.the engine goes to a rough idle? turn the control knob to off and the engine runs smooth when idling in gear???

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Is the heater fan on when HVAC controls are turned on? Just double check that AC isn't turning on, open hood and watch compressor clutch. Verify it's not engaging . Possible fan lost could drag down alternator and put load on engine


i will check if the fan is turning on !cooling and heating works fine when turned on never checked fan?will do this now!get back to you and thanks.


checked fan.all is working well.when fan comes on ,rough idling?when fan goes off because i turn knob to off.smooth idle?would that make problem idle control valveonly???

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I have a similar issue, I have a 2001 4dr Ford Escort 2.0, I found out that when I have the ac, heater fan off, ac fan to head n heater fan to feet, it won't revive every 5 seconds on a stop or red light. However, it will revive every 5 seconds for a second or two when on ac, max ac, heater fan to head n feet and window and feet. What could be causing reviving every 5 seconds lasting 1-2 seconds when in those ac or heater settings?

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I have pretty much the same thing with our 2004 Escape V6 XLT. When we are at at stop light if the heater fan is on even low and the engine fan turns on it drops the idle to about 400 RPM's...I have check and made sure the AC is off and set everything to the off positions. When it drop's the idle low i turn off the heater and the idle goes back up where it belongs. Whats up I tested the Alternator and The battery all good.


My 2000 Ford Escort started with a similar problem three (3) years ago. The engine develops a rough idle when I come to a stop, if the A/C is on, it gets worst. I have replaced the Idle Control Valve, Idle Control Sensor, MAS Sensor, Motor/Transmission Mounts, Oxygen Sensors and cleaned the Engine Air Control Valve. The car continues with the same problem! It runs great otherwise, so I have decided to ignore the rough idle at stops and minimize it by shifting to neutral.

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My 2002 ZX2 does exact same thing and do the same living in vegas at a light put it in neutral there has got to be a answer have had 3 different ICS had intake manifold gasket replaced now has seem to idle ruff with headlights and heater on not defrost but put at 1200 rpm smooths right out or put in neutral. turned idle up but that turns on check engine light.????


Yes, I even tried turning up the idle which made the engine run better when I came to a stop, but then the check engine light came on. As I said, I am not worrying about it any more, I just shift to neutral when I come to a red light and the a/c is on.

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