Any time I come across an interesting car problem which I end up solving, I like to share my experiences with the community which will hopefully help someone else out there having similar issues.
Last week I came across a situation where a 2007 Acura TSX with around 90K miles was having severe drivability problems with very poor idle where the car would turn off if I did not press gas pedal, CEL, VSA Module & Emissions messages simultaneously flashing. Idle problems would disappear if I was able to rev past 3000 RPM but poor idle would resume once the RPM dropped to 1000.
First thing i did was to pull the CEL Code which was P2647. Looking it up in the service manual, it mentioned the VTEC pressure switch being high (meaning it was reading high pressure). My first thoughts were that it was most likely an oil issue (too much oil) or a bad pressure switch. However, I could not understand why a bad pressure switch would cause all of these symptoms simultaneously at idle. The service manual stated to test the pressure switch which turned up to be fine so why was the ECU reading high on the pressure switch? Faulty ECU perhaps? a short?
Everything pointed to an electrical problem taking into account the numerous system malfunctions and piss poor idle. However, I decided to pull off the VTEC solenoid assembly to check mechanical malfunctions before diving into the dreaded electrical malfunctions. This is what I found after pulling off the VTEC solenoid assembly:
The burned on oil deposits were horrid! Upon closer inspection, I noticed that the piston valve that controls oil flow to the cams was seized up in the open position! (VTEC ALL THE TIME BRO!) It didn't take long to find out the reason behind this from all the burned on oil depots and sludge. What had happened was that enough deposits were accumulated around the shaft and piston which increased the diameter ever so slightly causing the shaft to bind up, sending constant oil pressure to the VTEC cams all the time. This explained the poor idle below 3000 RPM and fine at higher RPMs.
From the ECU's standpoint, the VTEC Pressure Switch was telling the ECU that "we're in VTEC mode now" but the ECU had not initiated the solenoid. I'm assuming this along with poor idle caused the system to go into safe mode causing the VSA and Emissions messages even though those systems had nothing to do with the problem.
My guess is that either poor quality oil was used or too infrequent oil changes caused these deposits to build up over time. The tolerances in the VTEC assembly are pretty fine.
The best bet would have been to replace the assembly since it's fairly inexpensive ($140) but I decided to clean it to see if I could get the function back. After half a can of parts cleaner and working the shaft with a pair of pliers, I was able to free it pretty nicely. Here's how it looked like after cleaning:
I would imagine a dirty VTEC solenoid assembly could potentially cause an intermittent bind which would have been more difficult to pinpoint so if you are getting a P2647 which comes and goes, I would open up that sucker and give it a good cleaning before changing any parts.
There's also quite a bit of discussion whether or not you should clean the VTEC solenoid. My answer to that is if you've purchased your car used, you have no idea how well maintained the car has been so it would be a good idea to give it a thought especially knowing how easy it is to remove. Just go buy the gasket ($5) because if you install it using the old gasket, there's a 90% chance it will leak.
To sum it up... Here are the symptoms of a seized VTEC solenoid piston valve.
Very poor idle at low RPM which clears up at high RPM, CEL P2647, VSA System Malfunction Message, Emissions System Malfunction Message, Engine Whine at idle (due to VTEC being engaged at all times)