Contour Enthusiasts Group Archives Forums General Troubleshooting Engine surges when defroster is on.

I searched the posts and found many surging issues, but none that solve my problem. I have a 2000 SVT Contour. When I turn on the defroster (front) the car starts to surge. It will also surge if I put the dial on defrost/floor or run the A/C. I chalked it up to the compressor pulling on the motor and normal operating, but it is starting to really drive me nuts....HELP!

Here is some stuff to think about.


The A/C compressor puts a load on the engine which of course slows it down. The PCM responds by trying to open the IAC to compensate and restore the RPM's. This will work as long as the mixture is correct. If it's too lean, not enough power is generated to keep the RPM's from falling.



So the A/C must be working and not put too much load on the engine.
The IAC must be working and not too restricted (TH fix).
The mixture must be correct. The mixture is affected by vacuum leaks, O2 sensors, the MAF, dirty injectors, and even the ECT.

Vacuum leaks can be external hoses, the PCV valve and fresh air hoses, the EGR valve, gaskets, or the intake tube between the MAF and TB.

The IMRC must also have the secondaries closed at idle.


If the CEL is on or has come on while driving, have the codes pulled and check the indicated problem first.

Your AC fluid is probably low. I just fixed this exact symptom. The AC compressor clutch is cutting on and off when it should stay engaged. (Open the hood and check it out...) Get a bottle of R134a and a filler hose with guage for $15 at NAPA. (best deal imo) Once the AC fluid pressure is correct the AC clutch will stay engaged (when the AC or defrost is on) and the surging stops.

refilling my AC fixed this problem for me as well.

mine was so bad that when the AC kicked on and the pavement was wet it would break the tires loose. kinda disconcerting at 75 on the highway.

good luck.

This is a common Contique quirk. Do a search it's been discussed in great length. The A/C compressor places a load on the engine, and as it cycles on and off, the load is thus removed/replaced.

...and the surge/bucking is worse than on any other a/c-equipped car I've ever owned, for some reason. But it doesn't seem to hurt anything, it's just mildly annoying.

i fixed mine...... by removing the a/c.