Engine/Tranny Shutter

Hey guys, Thought I'd leave a post here too and see if anyone has an idea. Need some help here. Just bought my first mustang two weeks ago. Shes a '02 sixer convertable with 38k miles. Always stored with a cover over her and indoors to boot so she looks great still. Didn't notice any issues during the test drive other than you feel every bump in the road through the suspension.

So the day after I bought it, I noticed that while accelerating through 30-45 mph it started jerking/surging. Felt like a really bad transmission shutter. Mechanic swore up and down that it was something simple so I replaced plugs and wires with the premium stuff, swapped the air filter and fuel filter, and had my mechanic clean the throttle body and air flow sensor. That helped it to an extent (took it from about a 10 to a 7 on a 0-10 scale). She idled much better though.

My mechanic still swore it wasn't trany related. He checked some engine codes (though no lights on) and found the EGR valve pressure sensor was out of spec. He swapped that out and it seemed to fix the issue! I was thrilled! Drove it around that night and it was fine. Then I went and put gas in it (speedway 87 octane), got a block down the road and BAM it starts it all up again. It started shuttering really hard during acceleration at the speeds listed above. My mechanic was stumped. It sounded like he had lost his patience for the issue and didn't want me to bring it back.

So now I'm trying to figure out what to try next. The mechanic said that driving it wont hurt it, just annoy the hell outta me. I put 5 gallons of 93 octane (BP brand) in it last night and it seems to have calmed the issue for the time being.

Any ideas? And what grade of gas do most people run in the V6 models?

Thanks for all your help fellas!
Paint

87 octane is what your engine calls for. 87 should be used.

You say it happens only when accelerating? Accelerating hard or moderately? Does it happen when you are maintaining speed on a level surface? If it happens mostly during light load operation at 30+ MPH, then it is an EGR/DPFE problem. I've experienced it in my car last summer and even after replacing the DPFE sensor (what your mechanic replaced) did not solve it. I could not figure it out and then one day it went away and never came back - until 2 days ago after some engine surgery - go figure.

First thing I would recommend is to troubleshoot the EGR/DPFE system a little further. On the top of the EGR valve is a vacuum line. Follow the vacuum line to the vacuum solenoid mounted next to the fuel rail. Remove the electrical connector from it. Start the engine up and drive it around. This will prevent the EGR valve from opening when the PCM commands it open.

If you can't get it to hesitate/surge any more, than the EGR/DPFE is confirmed as the problem. You can keep this disconnected, but I would not recommend it as more than a temporary fix.

Some other checks include the two rubber tubes connected to the DPFE sensor. I believe in the Mustangs, it is on the rear of the driver's side head. It is on whichever side the EGR valve is on. It is a tight fit in there, but if you can get to it, there is an electrical connector on it, and two rubber tubes connected to the bottom. Make sure they're on tight and if you can visually see, make sure the other ends are on tight to the EGR tube which extends from the exhaust manifold.

Here's what the DPFE sensor looks like:
http://rockledge.home.comcast.net/~rockledge/DPFE_Plastic.jpg

And here's what the EGR valve looks like.
http://www.carpartswholesale.com/images/cpw_domestic/thumbs200/motorcraft/egrvalve.jpg