by Snappy » Tue Jul 01, 2014 7:27 pm
Hey Guys,
I've been reading this post for some time now (over the last 6 months) as I developed the same problem of flat spotting from 2200 to 3300rpm - outside of this rev band the car was fine, but like yourselves a horrible car to drive in and around the city. Found that resetting the ECU (by unplugging the battery for a period of time and reconnecting) the flat spot would be resolved for an arbitrary amount of time - could be 2 days or 5 weeks, before returning.
My mate is a motor mechanic and he hooked up his diagnostic tool, but failed to report any error codes - so he suggested changing out the O2 sensors; clean the MAF sensor - did that and the flat spotting went away for some weeks....before returning.
All the things that you guys had suggested I had tried: changing out the O2 sensors, cleaning MAF, replace fuel filter, replace spark plugs, including changing fuel suppliers (I have always used premium 98 since new) and anything else I could think of that was fuel delivery system / engine sensor related to no avail. Instead of continuing to replace items that may not be guilty of any wrong doing, I ended up booking into Subaru to see if they could diagnose the fault - I was very hesitant to do this as the charge was $155 per hour and every hour afterwards! But, this was my last attempt to try to resolve the issue before I sold the car out of pure frustration!
I took the car into McGrath Subaru at Liverpool and the guys there were excellent! They did some conservative checks/replacement of items first (eg. fuel filter) test drove the vehicle, found out that this did not resolve the issue, so next step was they hooked up their laptop to collect some realtime data. The guys collected about 10mins of drive data before sending it off to Subaru Australia where they analysed the data and reported back (which you guys have mentioned) that the ignition timing was being retarded between the 2200 to 3300 rpm range. Subaru Australia immediately knew what the issue was and advised that the 2.0R engine has two OCV (Oil Control Valves) that control the ignition timing for the variable valve timing and that these were most likely faulty and not allowing the timing to advance. They replaced two OCV (as both had failed) and I drove the car home and it was fine! Hooray! I couldn't tell you happy I was to drive a car without that hesitation!!!!
A couple of days later I drove the car on a long distance trip and the car was fine and drove the car back...then the issue came back again! My joy had now returned to frustration as I'd thought the issue may have been resolved once and for all! I gave McGraths a call and they said 'no probs, bring it in and we'll check it out' - took the car in and the guys hooked up their laptop again to collect drive data; sent away to Subaru Australia and was advised that one of the OCV had failed! Subaru replaced the failed new part under warranty and I've not had an issue with hesitation since (touch wood) having this done which was a couple of months ago. I refrained from posting a reply as I wanted to make sure that the second OCV replacement actually did resolve the issue.
I can't tell you how good it is to drive this car now! My recommendation is to take your car into Subaru (McGraths Liverpool I would highly recommend) for these trickier types of issues as they have the advanced tools and resources to investigate the issue...I had only wished I'd done this earlier!!
Hope this post helps!