2003 Ria rio rough idle when air con is on, idles fine if aircon is off. What could cause this?

have oil pressure done ,oil pump could be going out.

This is most likely caused from the idle air controller. IT is most likely dirty or sticking.

Sounds like the compressor is failing or seized (for the air con). This would put extra pressure on the system. It could be another fault with the air con system like the solenoids not opening up to allow the flow of gas in the system.

It can be issue with low fuel pressure,the fuel pump is getting old both needs to be checked.Also get the IAC valve checked.
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These details will help.
Thanks.

1997 escort idles rough, the first thing is to make sure the throtlebody plate is clean. This sounds like the idle may be staying to low at times if it smooths out with ac on, when the ac is turnned on the computer raises the idle a touch to make up for the strain on the engine from the ac compressor, clean throtlebody and look at and clean idle air control valve, if this valve is not controlling the idle when needed the engine will idle lower than normal and cause a rough idle.
Another thing is the sparkplug wires, take a look at those, if at night or with a good eye use a spray bottle and spray a mist over the wires and watch for any sparking, this spark may be very small so look at each wire closely or may be big enough to see and hear. this is where i would start. good day.

Hello! Most probable cause is a leak in the vacuum line or broken elbow connection to the Positive Crankcase Ventilation (PCV) valve...Check PCV and its vacuum line...Send results...

Guru..............saailer

I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

if it idles rough when air con is turnd on ur idle my be running to low to start with the air con is a pump and will take power from the engine and wen u turn on ur air con there is a clutch on ur pump witch engages witch will couse the revs to drop

My personnel fix for this.

Here are some of the causes of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

has anyone checked for a vacum leak? a vacum leak will cause rough idle at idle. check the lines from the pcv valve.

I know that this will sound Stupid. Change the Fuel Cap. If the Seal on the Gas Cap is Bad it will allow Air to get into the Fuel tank and cause your Rough Idle.