SamInCleveland

2005 V6 4.0L Mustang
No custom tunes
No mods

Over the past 3 weeks I've changed:
MAF Sensor
TPS
Throttle Actuator (on the TB)
And yesterday, I installed a new BBK Throttle Body.

Some history...

From the day I bought it, it always needed a good warm up, no matter the season, to idle smoothly. Otherwise while coming to a stop in neutral (unless I have the clutch in) the RPMs would surge up to 2500, up and down Until I came to a complete stop.

About a month ago while driving on the highway about 60mph, I got a sudden "dip" in the acceleration as though it had almost stalled. The next day it happened again, then while getting back onto the highway at around 40mph it dipped again then went into failsafe mode.

I've done all of the above, checking codes and reading advice online.

Alas, after changing the Throttle Body yesterday the surging while coming to a stop became worse... going to nearly 3000 RPMs until I came to a complete stop. And when I went to the store this morning it went into failsafe mode again.

I guess my next attempt will include a new fuel filter and a tank with Sea Foam.

Any advice on how to look for / find vacuum leaks, as well as any other advice would be greatly appreciated.

I love this car and would hate to give up and go car shopping again!

66and06stangs

Hmmmm... I see BBK and I just have to say hmmmmm. I put a BBK CAI on my car an I have a problem that, let's see, probably on the 10th set of tunes, probably 6 or 7 datalogs, and I still have the same problem. Similar to yours, except mine does this - when I come to a stop light (or sign), I clutch the car and come to an idle. If I have to inch forward at all, my car will down rev from idle (somewhere around 700rpms) to sometimes almost dying. I cannot stand the sound my motor makes. I just got my latest "fix" tune over the weekend and drove it today... and yes, it does the same thing. The BBK kit had me hack into the breather hose, and I have gunked it up with all kinds of stuff to seal it. It acts like a vacuum leak but I've spent several cans of carb cleaner trying to see if I can make my motor skip.
I thought I would give it one last try - I went to Ford and paid the almost 100 bucks for a new hose so I can go back to my stock air cleaner setup. If my car runs good with the original tunes I got with the original air cleaner, I'm going to throw this BBK thing in the garbage. I may find that my car has something else wrong and the behavior has nothing to do with the BBK CAI.... I'm about to find out.
I did not mean to hijack your thread. I will be watching responses closely. As you do, I would like to see any/all approaches on vacuum leak investigation!

SamInCleveland

Yeah, the BBK TB was installed well after all this started.
I'm still kind of stuck on this, with no idea what to try next.

SamInCleveland

By the way, your issue sounds like it could be either your TPS or the actuator. Like something causing the butterfly to close up at lower idle?
I'd trade your issue for mine, hehe.

66and06stangs

I've been fighting my issue for almost a year... yeah, i'll trade you, lol. I drove it home last night, there was a wreck so I had to do a bunch of stop'n'go. My car just about died 50 times doing the down idle thing... argh. I emailed Bama again, I'm waiting to see what my tech says. I'm ready to throw that thing away. I did look at the AirRaid CAI... now that one looks good. It utilizes the stock breather hose, no hacking whatsoever.

66and06stangs

Well, I do not see anyone else jumping in on finding a vacuum leak, so here is what I did - 3 separate times I got a can of carb cleaner. With a warm, running engine I sprayed the carb cleaner on each joint, listening for an engine miss. After the first time, when I gooped everything up with black gasket gunk (yes, it looks like hell), I simply do not get my motor to shudder. I don't know what else to check. I do have a vacuum guage for my older Stang, I guess I'll start googling about how to isolate a vaccum leak on a newer Stang...

SamInCleveland

Have you tried reverting back to the stock intake system to see if the problem still exists?
If anything, just so it's more drivable until you get things worked out.

I cannot drive mine at all. Last I tried to take a short run to the store I got to the end of my street and went into failsafe mode again.

After replacing multiple sensors and the TB itself, I'm stuck in the same place I was in the beginning, only worse because for now it's the only ride I have. :|

Derf00

You mentioned reading codes but didn't mention what they were (if any)?

have you tried datalogging with a tuner or even having a tuner connected to see if you can check it while its running in failsafe?

How do all of your plugs look?

66and06stangs

I am jaded I guess, but I'd get that BBK tb off and go back to stock. I had a similar problem in Hawaii (lived there for just under 2 years). The gas there is terrible and I had to clean the throttle body assy twice while there. I also replaced the TPS which was so gunked up when I took it off. Fuel filter (you already mentioned) and a bottle of Techron. When I first moved here to Florida I was having a problem, the gas here has a high amount of something and I was told to run a bottle of Techron in the car about once every six months. Again, I told you my basic way to look for a vaccuum leak, I'd like to hear about how someone else goes about checking for one.

66and06stangs

That is exactly what my plan is now. Bama agrees that something with the CAI is doing this and I'm going to A) revert back to my stock intake, and B) run the stock program for a bit... I know I'll hate it but want to prove/disprove that the problem is with that CAI. If no problems, I'll put the original street tune that Bama gave me, that made my car really, really fun to drive. If no problems then, I'm going back to American Muscle to see if they'll do something to help me out. Love the sound the CAI gives the car, but the year of trouble I've had... man. I'm still thinking about your problem too...