idle with aircon on going up and down - 3200

[bossemaserati]

evening everyone,

i wanted to call on the forums expertise again:

when at idle my car, a 2001 3200 automatic, with the air condition on, experiences revs going up and down.
i have uploaded a video to youtube:

https://youtu.be/_VfvrmsuF2s

as soon as i turn the ac off, revs return to normal, here is another video:

https://youtu.be/eMN9wg4BWWQ

the pedal potentiometer is contact less, and also the throttle body is contact less and throttle response is excellent.

it also does not result in a CEL

at the last service, i asked the mechanics to check for air leaks, and they said they could not find any...

then i read in a post on the forum recently it was recommended to change the crank sensors as these are supposed to measure the revs and tell the ECU to adjust accordingly if the aircon is switched on?

do you think that would be the next logical thing for me to do?

thank you so much!!

bosse

 

[davy83]

The problem is the idle speed is too low. It should be bang on 1000 or a little above. So the uneven idle with the aircon i suspect is not connected to the aircon, but rather the fact its idling low. I would try changing out the crank sensor, as it is used to control idle speed, that would be my first suggestion. I had idle problems and it was down to the crank sensor and no warning lights so its possible.

If its not the crank sensor then the obvious throttle body question comes to mind? is it an original throttle body?

 

[conaero]

The usual airleak that you get on 3200's is the plenum bellypan gasket on the underside. The screws work themselves loose and fall into the V of the block then the gasket gets sucked in but the idle goes very wrong and up around 2.5k rpm then pulses up and down with a hissing noise.

So that said I don't bekeive this is it and Davy's suggestion is more probable in this instance.

 

[StuartW]

As it has the contactless throttle body, it does indeed sound like the crank sensor. I had it on mine too

 

[Contigo]

Crank sensor or knock sensor.

 

[davy83]

I am not sure the knock sensors are used when its idling? i thought they just got to work once you open the throttle and its starts trying to get power, and advances the ignition, and uses the knock sensors to get the advance just right? might be wrong, but i don't think my car had problems at idle when the knock sensors went.

 

[bossemaserati]

thank you everyone for the replies.
i did some more research last night and found this:

https://youtu.be/obUAQNwQERI

and thought i give it a go

this morning went to halfords and bought this:

http://www.halfords.com/motoring/en...ynns-fuel-injection-carburettor-cleaner-500ml

cleaned the throttle body from the inside (it was surprisingly dirty actually) and now it feels a bit better, but its not gone...

so crank sensors next! has anyone on here changed the sensor themselves? it it an easy diy job? thanks!!

 

[Contigo]

Yes Liam did his recently. Not too bad a job really, just a little difficult to get to.

 

[Contigo]

 

[davy83]

its a bit fiddly to get at, i seem to think the oil filler tube gets in the way. its easy enough to change out though and its a fairly cheap part too.

 

[bossemaserati]

Thanks for the help! Sensor is on order from eurospares... Fingers crossed it will work. Thanks!!

 

[conaero]

Its even cheaper if you buy the equivelent Alfa part, it slips my mind which model Alfa its off.

 

[Rex B]

Be sure to set the gap between the sensor and the pulley teeth correctly it should be 0.6 mm with a tolerance of +0.4mm and -0.2mm. You can also measure the resistance of the sensor which should be 650 ohms plus or minus 10% at 20c.

Rex B
Manual 3200