Engine revs drop

Chris139 · Sep 19th, 2003, 20:16

Occasionally , when the engine is at idle, the revs will drop by about 200rpm for a split second and then recover. It's just long enough for that "Oh no, it's going to die" feeling. At first I thought it was connected to the gearbox and something to do with engaging/disengaging the gears, but it has happended in Neutral. It's almost like there is a sudden power requirement, like the air-con being turned on or the cooling fans suddenly switching on. I have also felt it whilst cruising. It has never actually died and always starts first time. It has done 97,000 miles.

It is a 2.5 20v auto V70

Any ideas anyone ?

Regards,

Chris Hampton

Sep 20th, 2003, 11:14

Hi Chris,
I've had this happen with my V70 2.5 20v T, it only happens occasionally but it is a bit frustrating. I thought mine was going to cut out but it never does. Sorry I haven't a clue what it is I assume it's meant to do it, I thought it may be the AC compressor swithching in? Maybe someone with some technical knowledge can help please as I would like to know as well.

Regards Paul

warthog · Sep 20th, 2003, 14:10

Hi,

the idle speed is kept constant by the Idle control valve controlled by the ECU. This is found in front of the right hand end of the inlet manifold hidden beneath the throttle linkage cover. My only suggestion is to clean the contacts of the electrical connector block attached to the valve.

On a previous car I had, I was plagued by an intermittant idle problem that only occured in the wet and then only after about 30 secs of engine running!! The engine would start to run rough and then slowly die away. It would always start again straight away, but I never got to the bottom of the problem and sold the car still suspecting a fault with the idle control valve.

Let us know how you get on.

Regards

Brian

Networkguy · Sep 20th, 2003, 22:32

It does sound like the air con kicking in.

Sit with the engine running and the window down and you should hear a click at the same time as the AC thingy does it's thing (can you tell I am not a mechanic).

Chris_Rogers · Sep 21st, 2003, 08:22

Suggest you remove the idle air valve from the car and clean it with carb cleaner, be careful not to get the cleaner in the motor.
It would be a good idea to clean the throttle body too, be careful not to get cleaner into the throttle position sensor.

Sep 19th, 2003, 20:16	#1
Chris139 Member Last Online: Feb 18th, 2010 15:52 Join Date: Dec 2002 Location: Stroud	Engine revs drop Occasionally , when the engine is at idle, the revs will drop by about 200rpm for a split second and then recover. It's just long enough for that "Oh no, it's going to die" feeling. At first I thought it was connected to the gearbox and something to do with engaging/disengaging the gears, but it has happended in Neutral. It's almost like there is a sudden power requirement, like the air-con being turned on or the cooling fans suddenly switching on. I have also felt it whilst cruising. It has never actually died and always starts first time. It has done 97,000 miles. It is a 2.5 20v auto V70 Any ideas anyone ? Regards, Chris Hampton __________________ Current:- 2004 S60 D5 S (163bhp) Geartronic 1994 855 2.0 20v GLT (140bhp) auto Previous:- 2000 S80 2.4 (170bhp) auto 1998 V70 2.5 (170bhp) auto

Sep 20th, 2003, 11:14	#2
medic94 Guest Location:	RE: Engine revs drop Hi Chris, I've had this happen with my V70 2.5 20v T, it only happens occasionally but it is a bit frustrating. I thought mine was going to cut out but it never does. Sorry I haven't a clue what it is I assume it's meant to do it, I thought it may be the AC compressor swithching in? Maybe someone with some technical knowledge can help please as I would like to know as well. Regards Paul

Sep 20th, 2003, 14:10	#3
warthog VOC Member Last Online: Oct 30th, 2021 14:51 Join Date: Dec 2001 Location: Bristol	RE: Engine revs drop Hi, the idle speed is kept constant by the Idle control valve controlled by the ECU. This is found in front of the right hand end of the inlet manifold hidden beneath the throttle linkage cover. My only suggestion is to clean the contacts of the electrical connector block attached to the valve. On a previous car I had, I was plagued by an intermittant idle problem that only occured in the wet and then only after about 30 secs of engine running!! The engine would start to run rough and then slowly die away. It would always start again straight away, but I never got to the bottom of the problem and sold the car still suspecting a fault with the idle control valve. Let us know how you get on. Regards Brian __________________ Brian '96 T5 Estate Auto

Sep 20th, 2003, 22:32	#4
Networkguy Senior Member Last Online: Sep 20th, 2022 19:25 Join Date: Nov 2000 Location: Lincolnshire	RE: Engine revs drop It does sound like the air con kicking in. Sit with the engine running and the window down and you should hear a click at the same time as the AC thingy does it's thing (can you tell I am not a mechanic).

Sep 21st, 2003, 08:22	#5
Chris_Rogers VOC Member Last Online: Apr 10th, 2017 16:55 Join Date: Jan 1970 Location: South Kent Coast	RE: Engine revs drop Suggest you remove the idle air valve from the car and clean it with carb cleaner, be careful not to get the cleaner in the motor. It would be a good idea to clean the throttle body too, be careful not to get cleaner into the throttle position sensor.

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