Engine surging 2.5 RS

Dave Adams · Post by **Dave Adams** » Wed Jul 16, 2008 4:30 pm

Hi

My first post - I recently bought my wife a 2001 RS Impreza with 2.5l motor and 5 speed manual.

Nice car with only 32,000k on clock.

However we have an annoying problem of engine surge when going down hill. I notice it mostly about 5-6 km from home on a long downhill slope (not real steep though). It also happens on other down hill slopes and almost feels as if it is getting too much fuel.

My wife reckons it feels like a cruise control that is trying to adjust speed but CC is off.

My only other complaint is the very high revs of about 3,000 in 5th gear at 110kph. It really feels like it is needing another gear. Is 5th gear a 1:1 ratio or overdrive?

thanks

Dave

chubby37 · Post by **chubby37** » Wed Jul 16, 2008 5:09 pm

you could have a dirty fuel filter....the revs sound about right in 5th..

steptoe · Post by **steptoe** » Thu Jul 17, 2008 12:05 pm

3000 at 110 ? sounds like a convert from a 'big thirsty' six used to seeing about 2000 at same speed, which is why i reckon there ain't that much difference in fuel consumption between a lot of fours and sixes.

What if you suddenly declutch and shove into neutral when it is surging, what happens to the idle then ?

Gremlins · Post by **Gremlins** » Thu Jul 17, 2008 1:31 pm

Are you actually on a steady throttle when it is surging or alternating between completely throttled off and slightly on throttle? I have an 06 Impreza that is an interesting drive on some downhill runs (usually gentle downhill runs at city speeds) as it's impossible to find a throttle setting to give a constant speed. Throttle right off, the thing slows down, open the throttle the smallest amount possible and it speeds up. Going down hill then consists of repeatedly alternating between fully off throttle and slightly on throttle to try and keep somewhere about the right speed. (Even the cruise control has to do this to try and keep a steady pace). This might not sound much of an issue but due to the often criticised lash in the Subaru manual AWD driveline you get a slight "jolt" everytime you transition between off throttle and on throttle and this can give the impression the vehicle is surging especially to passengers who don't know what's being done with the throttle pedal. From discussions with other Impreza drivers it appears this characteristic is not isolated to my vehicle (read: not much you can do about it).

Post by **Alex** » Thu Jul 17, 2008 2:59 pm

chubby37 wrote:you could have a dirty fuel filter....the revs sound about right in 5th..

agreed. That was my first thought.

alex

Dave Adams · Post by **Dave Adams** » Mon Jul 21, 2008 4:23 pm

I would not have thought it was a dirty filter as there is no issue at higher speed. The car has plenty of power so I would not think it was fuel starvation.

I am starting to think it might be sensitive throttle as one poster said. Never had the problem with any of the other 15 or so cars I have owned from little 1100cc Corollas up to 5 litre V8s. And yeah last few have been big lazy sixes so speed per 1,000 revs was noticeable. I still reckon Subaru would be better with a sixth speed though.

Then again when I can now corner on rails compared to driving the big six that handled like a wheeelbarrow of wet cement then I have liitle to complain about.

It is due a service in about 5,000k so I will get it checked then.