Power/Revs Pulsing
 

Howya folks?

Only recently bought a 2005 Forester 2.0 XT
The car was lying up for a couple of weeks due to a wee ding, but since I got her back today I've had a strange problem.

The Power / Revs are pulsing
I can notice it when driving along the car is surgung/lagging/surging both when driving normally and when in cruise control
Also when I'm sitting idling there is a slight pulse
If I increase the revs to 1.5K she pulses around regularly i.e. rythmical steady rate (approx 30 times / min)
If I increase the revs to 2K she does the same but a couple of more pulses per min
And if I increase the revs to 2.5K, same again but a couple of more pulses than that

Panel beater that repaired the car reckoned dirty injector, so I popped in a bottle of injector cleaner into half tank of petrol

A buddy of mine has had similar problems with different cars and he reckons Throttle Body.

I rang a car diagnostic Co and he reckons no point putting her on diagnostics unless theres an engine management light (which there's not)

Anybody any ideas on where my problem might lie?

Thanks in advance.

Garry

Slow (starting to fail) lambda sensor is rather likely.

Should that show up on diagnostic check?

Eventually it may do but I couldn't tell you for sure on a 2005 car. Have you ever seen the EML come on? If so then a code would be logged which would help diagnosing the problem.

It seems to be leaning on the lambda readings going by what you say and as it cycles between lean/rich you get the power surge. Typically you get a few crossings per second and don't feel the pulsing, but as they slow you get less crossings and its more noticeable. Not sure on your year but you may only properly get rid of the feeling completely with a remap as I know the MY99 and MY00 cars tend to just follow the lambda sensor reading and quite often surge even when the lambda sensor is new.

Obviously the sensor is expensive, you could try driving it without it connected for a bit and see if that is better. This then uses basic fuel trim without using the relying on a slow(or bad) lambda sensor. However this would likely cause the EML to come on which would have to be reset via diagnostics connector.

Try cleaning the boost solenoid we had the same with ours, not noticeable at idle but definately when driving and it's free!

Lads .... just getting back to this now...a mechanic let me down so had to go to another who reckons lambda sensor
Problem is that the part number isn't readable on the original part and Subaru dealers won't give the part number
Anyone on here able to chase the part no for me if I can give you the chassis number