Engine revving need help

[Sampson]

My brothers dc5r is revving to 2000-3000 rpm then dropping to around 600 rpm then revving again over and over he was away for 6 mths in the gulf car was regularly started but no driving he is on his 2nd to 3rd tank of fuel has but in octane boost and injector cleaner still not fix. before he left he put fuel sabiliser to help stop the fuel from going off. Any help would be great and any recommendations for a good place to take the honda to in sydney.
thanks

[m0nty]

Its the air flow sensor. Super common fault on DC5s.

[TODA AU]

My brothers dc5r is revving to 2000-3000 rpm then dropping to around 600 rpm then revving again over and over he was away for 6 mths in the gulf car was regularly started but no driving he is on his 2nd to 3rd tank of fuel has but in octane boost and injector cleaner still not fix. before he left he put fuel sabiliser to help stop the fuel from going off. Any help would be great and any recommendations for a good place to take the honda to in sydney.
thanks

Sounds like a vacuum leak,
If the car has basicly sat dormant for 6 months, it may be a simble as a gammy IACV & a can of carby cleaner will sort it out.
The rise in reves is increased airflow past the throttle,
The sharp drop is the over-run fuel cut comming in...
From this you know 2 things, the TPS is likley correctly adjusted casue when it's out or open, the over run cut doesn't always come in.
The MAP sensor is likley OK, as the car revs up & down smoothly, LOL.
(NB: When the Map sensor fails, you'll have black smoke out the bum)
So, before you spend any money,
Check the PCV hose (left hand side of I/M)
Check the brake booster hose
Buy a can of carby cleaner & with the engine running, spray some arount the intake manifold & fiitings etc... If no change in engine running (should near stall if you spray a leak) , remove the intake pipe & clean the IAVC (Port in lower side of throttle) again, just spray in some carb cleaner & run the engine. See if it gets any better. If it does, go & buy a can of Subaru upper engine cleaner & use that. I could be wrong, but chances are this is more than likley your boggle.
If an aftermarket throttle is fitted together with RBC/RRC etc...
You may have a wiring issue due to poor clearence with radiator shroud & strong tension on the loom. This may have failed over time also.
Hope that helps.

Its the air flow sensor. Super common fault on DC5s.

I think Sam meant to say MAP sensor.
Both MAP & TPS are notorius for failures on DC5's

[Sampson]

Thankyou for your help greatly appreciated