stang73

I own an '08 Mustang GT convertible 4.6L automatic trans. When the air temp is cold, about 40 degrees and lower, and the engine is cold, it will surge when I accelerate. It will do this with just a very slight amount of throttle but if I add a lot of gas it does not surge. It will not surge if I just let it idle but begins when I start to accelerate. It will keep doing this for about 1 minute or less then clears up. This is definitely an engine surge and not transmission related. Oh yeah, and it doesn't always happen. Anybody have any ideas?

CatSkinner

No codes?
I realize this is not at idle, but try cleaning the throttle assembly for a start and see what happens. This link progressively takes you through cleaning the throttle body, IAC, MAF, and the TPS as well as setting the base idle.The TPS is really what might be giving you the issue.

http://www.muscularmustangs.com/iac.php

__________________
Prius repellant, just add gas.

stang73

There are no codes set probably because this only happens out of closed loop, when it's not being controlled by the computer, as I understand it. I will go ahead and clean the throttle body, although I only have 12k miles on it and it's been happening almost since new. I didn't want to bring it back to the dealer and get into that b.s. If it were the TPS wouldn't it happen all the time? This problem is intermittent and only when OAT is about 40 degrees or below, never during the summer.

CatSkinner

Good point, since temperature seems to be a factor, I'd be looking more at the MAF instead, not sure if they looked at temperature as well on a stock 08, but cooler temps have denser air which will be a factor.
Part 5 of the link I sent has the procedures for the MAF, Ford Mustang MAF - Solving your idle problems
Even though this is a prior generation from your pony, the basic procedure still applies.

Temperature (due to expansion and contraction) could be causing something in the throttle body to become a little sticky which might also cause improper changes in control until you've opened up on the throttle more. Without the ability to monitor everything that's actually happening while you drive, it's difficult to pinpoint exactly what's giving you the bug. The best thing in this case is to bring everything in the throttle body back to it's best working condition, then sort out what's left. The only other thing that mey cause a surge would be a vacuum leak, but that's usually just at idle, but since this occurs just at very low throttle, I'd stick that thought on the back burner, but not throw it out entirely.

Could you clarify something? Is this an 08 with 12K total miles or is that all you've put on it?

__________________
Prius repellant, just add gas.

stang73

That's 12K miles total. I bought the car new. It's so low because I have two other Mustangs that I "play" with. I have a '65 GT clone convertible and a '73 Mach 1 that I've owned since new. I restored it and did the show thing with it for a number of years. It also appeared in an article in Mustang Monthly a number of years ago. There is no reason I "need" the '08 but it seemed to be calling my name one day when I walked into the dealership to look at a Bullitt Mustang they had on display. I gotta say it is fun to drive.

CatSkinner

Ok, now I'm jealous. Love the Mustang's, had a 72, but it needed more restoration work than I could handle at the time, so I let her go.

BTW, Bedford's a nice town, very moving D-Day Memorial.

__________________
Prius repellant, just add gas.