Subaru lumpy when gently accelerating

[Matt]

Car: 1996 Subaru Liberty (Legacy) all wheel drive with the EJ22 engine (automatic) with 230,000km (143,000m)

When the car is cold and i gently accelerate from a stop it feels almost like driving over a bumpy road (lumpy acceleration? but no hesitation), however if i put my foot into it and accelerate firmly/harshly it responds and accelerates perfect, and revving the engine seems normal (both cold and warm)

I get no check engine light and no codes – nothing

I have already checked/cleaned: fuel filter, spark plugs, idle air control valve, coolant temperature sensor (reads cold temps fine), PCV, MAF (cleaned with CRC MAF cleaner) and TPS (responds correctly)

I have just replaced the ATF (simple empty and replace fluid, not a full flush or cycle etc – same problem) and about to replace the filter and thinking about replacing the fluid again + adding Lucas stop slip

The knock sensor is cracked so i have ordered a replacement one but when i disconnect it and drive the car (with a check engine light present because of it) it does the same thing

Any other suggestions?

Topic

[EricTheCarGuy]

Hard to say. It kinda sounds like a driveline issue to me. Good call changing the transmission fluid. I guess after you do the Lucas let us know if the problem changes or goes away. If it does, you’ve found the issue. If not, it could be an engine performance problem. I’m not going to say the knock sensor is a problem. I would think that if it was, you’d have a CEL for it. This article may also be helpful.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

Good luck and keep us posted.

[Matt]

I replaced the filter and added Lucas stop slip to the transmission today and did some more testing

While running the engine and getting the transmission fluid to the right level i also let the engine warm up to normal operating temperature first before going for a drive, still did the same old rough light acceleration which makes me think its transmission related rather then engine related since the engine was warm this time

Ill post back in a week or so with some results

Oh and keep up the good work Eric love your videos big inspiration

[EricTheCarGuy]

Cool, thanks for the update. Keep us posted on your progress.

[Author]

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