nelly_stang

I bought a used 2005 V6 Mustang about early 2008. It soon began stumbling at idle which produced a check engine light. I took it in and was told engine light was due to many misfire codes. The certified shop replaced my plugs, wires and coil. It still had occasional stumble at idle. Approx one week later, my battery went dead and I replaced it. After new battery was installed the car ran fine for 6 months.

It has now began to misfire-stumble more than ever before. I took it to Ford who quoted new throttle body assembly, fuel filter, and coil. Disgusted at the price, I took it back to certified shop from last year. They found the plug wires were arcing out the side causing the misfire. They have since replaced these wires under warranty and replaced my fuel filter.

However, car is still stumbling at idle (down to 300 rpm or so as if it wants to die, then going back up. up and down, up and down). The check engine light has not come back on, only occasionally flashed while driving down highway, but does not stay on. Turn the car off and restart- no engine light.

Has anyone come across this previously. Surely the entire throttle body does not need replaced- it must be a sensor or something. So far I have invested over $1K in getting car tuned up over last year and a half and am still chasing the same stumble or misfire with no resolution to date...

tx_zstang

You wouldn't happen to be a red vert, would you, with custom plates similar to your screen name? If so, I was behind you for a brief time

Anyways, sorry to hear all this. Several things come to mind, most of which you've already taken care of, but I'll list them anyway.
First, plugs and wires. My plugs/wires started doing that after about 25K miles. Replaced them and haven't had a problem since.
Second, many people will recommend cleaning the MAF, and that would be a decent thing to do.
Third, if the air filter has not been changed, change it. Although that shouldn't affect idle that much.
Fourth, you could also have a vacuum leak or an issue with the pcv valve, especially since the issues appear to be during idling.

The throttle body has caused numerous issues as well, and yours could be sticking or not operating properly. Do some research here and you'll see numerous tb-related posts.

Good luck!

nelly_stang

Thanks for information. No, no custom plates- Blue Mustang that roams D/FW metroplex.

When I stated it still stumbled after my full tune up, but prior to battery dying..I had taken it back to that shop at which time they cleaned the mass air flow sensor. So that was done and no luck. The air filter was changed when I bought the car to a K&N. I will take note of the pcv valve or vacuum leak though.
I do feel misfire while at speed though. Wether I have throttle control or wether cruise is engaged, I can feel it tug off and on like a misfire. But it does not disengage the cruise. But it is definately much worse during idle. Not necessarily on a cold start though. During a hot day where car has been baking outside or after 30 miles of driving and then slowing down to red light or stop sign it will start.

From reading around there are numerous suggestions based on posts for similar problems. An article I may run past my mechanic is at http://articles.d-tips.com/art8.html
This basically states a number of any malfunctioning sensors in the electronic throttle control system, can cause the PCM to make the car misfire.

Well thanks again for input.

up_yours_7

I have had this similar problem with my cruise that just started doing it but only when I would give it gas or up a hill on downhill or when it didn't need gas it acts fine

BWfVA

Just every once in a blue moon mine will studer going up a hill and it bugs the living heck outta me and I cant figure out what it is

nelly_stang

I took it to another mechanic last night and believe we found one issue. the throttle actuator control motor (TAC). The female plug/sensor will not connect 100%. It sits on the male receiver but the red pin will not engage to lock it. Theory is this vibrates or jiggles while car is running, causing my idle to go haywire.
From reading more about it, says it can cause your plugs to foul also. However, Ford does not supply or sell these female plugs according to the dealership parts department I called.

Anyone have any good leads as to experience with the TAC or know where I can buy aftermarket sensor/female connection? i have tried many websites but cannot find these connections/plugs for sale. This includes all the connections/plugs that are connected to the throttle body. Who sells them??