Car jerks and shudders at 40mph around 1500rpm

[Legacylight]

Hey guys

I have a 1999 Subaru Legacy BE5. For the past couple of years I’ve been having a jerk/ shudder when running on low rpms specially at 40mph on 1500rpm. It feels like the car hesitates/ jerks forward backwards. 
 

Ive tried everything from changing the tps, maf sensor, prop shaft, gear box, rear diff, egr, Idle sensor, injectors, throttle body cleaning, rear bushings etc but to no avail.

Would be great if anyone could shed a light to what this problem might be.

 

 

[el_freddo]

“Lugging” the engine. 

It will coast at those revs ok, but it won’t really like to pull speed from those revs in a high gear. 

Try changing down a gear at that speed to increase revs and see if that changes anything. 

If it persists I’d be looking at spark plugs, then leads, then the coil pack - one at a time to hopefully save money and identify the actual problem. 

Cheers 

Bennie

[Legacylight]

2 hours ago, el_freddo said:

“Lugging” the engine. 

It will coast at those revs ok, but it won’t really like to pull speed from those revs in a high gear. 

Try changing down a gear at that speed to increase revs and see if that changes anything. 

If it persists I’d be looking at spark plugs, then leads, then the coil pack - one at a time to hopefully save money and identify the actual problem. 

Cheers 

Bennie

Hey Bennie

Thanks man. I’ve tried downshifting and as the engine revs up the issue disappears. 
 

Does this mean I should avoid cruising at those speeds on lower rpms? 
 

Thanks heaps for your help.

Wicky 

[el_freddo]

That’s what I’d recommend. These engines don’t like high loads at low revs. 2000 rpm is the lowest you want to load the engine at. 

Cheers 

Bennie

[heartless]

if this is a manual, yeah, downshift..

cruising rpms should be in the 2500-3000rpm range.. 1500 is way too low

[forester2002s]

The EJ25 engines typically have peak torque at around 4000 r/min.  And torque drops off quickly below 2000 r/min.

So I tend to keep the engine speed between 2000 and 4000 r/min (for my style of driving, there's rarely any need to go higher than 4000).

[el_freddo]

I tested this out in my sister’s Gen3 RX 2.5 manual. Pulling 1500rpm in 5th is ~50km/h, which from memory is near 40m/h. 

Her car pulled up from1500rpm without hesitation. It did it slowly though and I didn’t bury the foot into the floor either. 

You may have an issue with your legacy - any stored codes? Check your engine mounts and the pitch stopper rod for wear too. 

Cheers 

Bennie