[Jeroen]

A few other questions;

Does the AC cool properly along the whole power band. (e.g. at any speed, engine RPM)

Does the engine idle properly at a steady RPMS or does it hunt a bit? (RPM going up and down a bit). If so, aux valve is likely suspect.

Is the current idle RPM normal? If that is a little low to start with, that could be a problem too.

If you can, do a full OBD scan, preferably with a manufacturer/model specific scanner.

I would suspect IAC or auxiliary air valve (not sure what term is used for the Santro.

That is the most straightforward explanation! Your AC puts an extra load on the engine. These devices are supposed to add a bit of air (and fuel) so your engine sticks to the same idle RPM under a slightly heavier load.

It is usually a problem with either the valve sticking or some air leaks across a seal. Especially the latter can be temperature related, so with a warm engine it could be worse than when your engine is still cold. It is/used to be a well known problem on all Ford Fiesta versions.

To get some idea if these valves are working not it can be checked very easily. let the engine idle, switch on the AC. Do you notice a dip in RPM that is not recovered within half a second? Something is wrong then.

If the IAC/Aux valve work properly, I would have the throttle body checked. Sometimes, due to wear and or dirt accumulating you might get similar problems

I am not sure how the AC is driven on your car. But if it is a belt driven AC, do check the condition of the belt and the tension. It can cause all sorts of erratic engine behaviour. Again, depending on the exact AC set up, a bearing that is on its way out can cause the same behaviour. But usually that will get worse over time, fairly quickly.

Good luck, let us know what you find eventually.

Jeroen

[KarthikK]

Originally Posted by CorollaDude

Mechanic replaced spark plugs, throttle body and some cable. Problem still persists. Losing confidence to take the car out now. What could the problem be? Please kindly help.

Get the Idle Air Control valve checked. One of my friends did face a somewhat similar issue on his car and he went through this grind to sort out the problem. IAC and throttle body cleaning did the job in his case.

[Swapnil4585]

I have the same question on my Corolla.

Certain facts: -

1. Ambient temperatures between 45 to 50.
2. 4 people in car and some small bags in the boot.
3. Car driven with AC on (normal cooling, no issue) for 4+ hours non-stop on the open highway. Speeds between 100 / 130.
4. No issues with coolant system.
5. No error codes on the scanner.
6. The air intake temperature shown by the scanner was 68 degrees, a bit abnormal for given condition.

Do I simply go and replace the air intake sensor? I have too many long drives to do.

[scorpian]

Originally Posted by Swapnil4585

I have the same question on my Corolla.
6. The air intake temperature shown by the scanner was 68 degrees, a bit abnormal for given condition.

The air Intake also gets heated up due to engine heat, so your sensor must not be at fault.
I usually get about the same readings in my car.
The air intake if place near a source away from heat will give lower readings.

[Swapnil4585]

Originally Posted by scorpian

The air Intake also gets heated up due to engine heat, so your sensor must not be at fault.
I usually get about the same readings in my car.
The air intake if place near a source away from heat will give lower readings.

Now on Monday and Tuesday, I again did a long 1100~ km trip during the day. Same non-stop driving at 100-120 kph, but completely without AC. The car performed flawlessly. In fact the fuel economy increased by a kilometer!