Can't seem to fix rough idle problem....HELP

[tpwarren]

I have a 2002 Mountaineer (4.0 AWD). I am have a rough idle all the time and decreased fuel economy and torque. I am getting NO engine codes so the dealerships are clueless. On rare occasions, it will die at the end of backing up. Now let me run through what I have done to try to fix the problem:

1. Got injectors cleaned. This had no effect and eventually the problem got a bit worse.
2. Replaced fuel filter. No effect.
3. Replaced spark plugs and wires. No effect - but when I was finished I didn't have a good connection on the number 5 cylinder. I ended up running on only five cylinders for about 5 minutes. I got NO engine codes from this which is amazing to me.
4. I figured that the oxygen sensor on the driver's side was out because of the lack of engine code. I replaced the front one which controls the air/fuel mixture. No effect.
5. I replaced the IAC valve. No effect.

I'm running out of ideas and the Dealership is of no help. YES, I AM GETTING GAS FROM DIFFERENT PLACES, SO IT IS NOT THAT.

Does anyone see value in replacing the rear driver's side O2 sensor? Could it be the fuel pump and what would be a good test for that?

Any help would be greatly appreciated.

 

[je5]

I have a 2002 Mountaineer (4.0 AWD). I am have a rough idle all the time and decreased fuel economy and torque. I am getting NO engine codes so the dealerships are clueless. On rare occasions, it will die at the end of backing up. Now let me run through what I have done to try to fix the problem:

1. Got injectors cleaned. This had no effect and eventually the problem got a bit worse.
2. Replaced fuel filter. No effect.
3. Replaced spark plugs and wires. No effect - but when I was finished I didn't have a good connection on the number 5 cylinder. I ended up running on only five cylinders for about 5 minutes. I got NO engine codes from this which is amazing to me.
4. I figured that the oxygen sensor on the driver's side was out because of the lack of engine code. I replaced the front one which controls the air/fuel mixture. No effect.
5. I replaced the IAC valve. No effect.

I'm running out of ideas and the Dealership is of no help. YES, I AM GETTING GAS FROM DIFFERENT PLACES, SO IT IS NOT THAT.

Does anyone see value in replacing the rear driver's side O2 sensor? Could it be the fuel pump and what would be a good test for that?

Any help would be greatly appreciated.

If you cannot make it store a code you may suspect a bad computer.

 

[BrooklynBay]

Welcome to this forum! I think your MAF sensor might have a dirt build up. Thoroughly clean out that mass air flow sensor, throttle body, and intake. Look in the useful threads section for a terrific article on cleaning all of this stuff up. They have very detailed pictures that you should find useful. Look under "cleaning your MAF sensor".

 

[aldive]

Have you scanned to determine the O2 senson(s) function?

 

[BrooklynBay]

Here is a link to a thread about cleaning one of them: Dead Link Removed I saw it repeated two times in the useful threads section. I was looking for a thread with pictures, but didn't see any in this thread. The information there is all that you would need. You could always do a search, since there are numerous threads about cleaning them.

 

[tpwarren]

Help so far.......

Thanks for all the responses. To answer some of the questions;

I was told by the dealership that the O2 sensors were working fine, but am hard headed and didn't believe them after the fact that the engine was running on 5 cylinders with no codes.

If the computer is bad, I would almost be tempted to trade the vehicle in. That sounds like a pricy fix.

I plan to look into the MAF cleaning and see if that helps. I know this engine is prone to these types of problems, but I think that it should be fixable........it ran smooth before.

 

[je5]

Thanks for all the responses. To answer some of the questions;

I was told by the dealership that the O2 sensors were working fine, but am hard headed and didn't believe them after the fact that the engine was running on 5 cylinders with no codes.

If the computer is bad, I would almost be tempted to trade the vehicle in. That sounds like a pricy fix.

I plan to look into the MAF cleaning and see if that helps. I know this engine is prone to these types of problems, but I think that it should be fixable........it ran smooth before.

Could you get the ID# of your engine computer?

 

[tpwarren]

Computer location

Where would I find the engine control computer ID number, or the engine control computer for that matter?

 

[brennenu4X4]

my car has the same problem. i was told by one of my friends that it is the fuel pump, b/c he said that the same thing happened to his brother and when he replaced the pump, it stoped. i have not tried it yet but i thought this may help.