Drop in Revs when AIR CON is on

[prelude_h22]

Hi Guys

Just noticed it this week as i have been using the lude for work as it has air con. The revs seem to drop really low almost to cutting out but it doesnt

It tends to occur when you come to a stop whilst pressing the brake.

I had this issue awhile back (without air con being on) and cleaned out the EGR and the IAVC (i think) valve which cured it

It doesnt happen when the air con is off - the revs settle normally with air con off

I know the air con compressor saps quite abit from the engine but surely it shouldnt cause the revs to drop really really low

Would it be worth cleaning the above valves again or is something else affecting it (i.e air con related)

it tends to drop to around 200rpm even a tad lower than that when air con is on and when i come to a stop (i.e. in trafic etc )
Hope you can help guys

Cheers All

[NCCMUR]

Mine does the same
Think its normal

[Merlin]

Yeah sounds pretty normal to me too, although my revs are not that low, especially if your car has 4WS. My revs have been pretty low on idle.

[judderod]

You might need to do an idle reset procedure by adjusting the idle screw. It involves disconnecting the IACV and setting a minimum rev. It's on the forum somewhere if you do a search. It's probably happening because the IACV is getting a bit old and tired.

[cebul]

You might need to do an idle reset procedure by adjusting the idle screw. It involves disconnecting the IACV and setting a minimum rev. It's on the forum somewhere if you do a search. It's probably happening because the IACV is getting a bit old and tired.

Exactly, disconect the IAVC, turn the scru to get roght revs and plug it back

[BMCC]

You might need to do an idle reset procedure by adjusting the idle screw. It involves disconnecting the IACV and setting a minimum rev. It's on the forum somewhere if you do a search. It's probably happening because the IACV is getting a bit old and tired.

This ^ manual states rpm sould be 790 +/- 50rpm when air con is on. see manual 11-115 part 10.

The ports etc get clogged over time and don't allow the same volume of air in compared to when the car was factory fresh.

[prelude_h22]

Crikey 790 RPM when the air con is on. Thats pretty high. So would that mean it should still attain that RPM even when i come to a stop and i press the brake - it shouldnt dip below 790rpm

With the idle adjustment screw i assume clockwise is opening the throttle (increasing revs) and anti clockwise is closing the throttle (lowering revs)

So on the procedure i assume at each stage 5, 8, 9 and 10 i should be adjusting the idle screw to meet the requirements at each stage

When you mean the IACV is getting old and tired - do people replace them easily or is it quite an expensive part?

Thanks again guys

[judderod]

I think that manual is for the US prelude which has an ELD hooked up to the ECU. UK cars don't have one, and I don't think JDM cars have one either. So the tolerances in step 9 and 10 may be wider.

Just go through the steps until step 8. That will probably sort it out.

If it's still idling too low under load, you might have to clean out the IACV again or maybe source a good 2nd hand one. You could also raise your base idle speed a little as per step 5 to about 600 - 700. A new IACV would set you back about £200!

[BMCC]

Not so much the Iacv just the ports for air in the throttle may get clogged over time so not enough air flows in through Iacv fitv and base idle screw. Check base idle and see if it is well off first.

[ADS1]

I think that manual is for the US prelude which has an ELD hooked up to the ECU. UK cars don't have one, and I don't think JDM cars have one either.

JDM cars do have ELD, or at least mine does.My revs would increase slightly when putting air con on. I dont have air con anymore, but same with headlights. When i switch them off at idle, revs drop slightly to normal.
Didn't realise uk cars dont have ELD.