Possible Vacuum Leak?

[Lazzman]

I have experienced some strange idle symptoms which I find puzzling.

Most people here know my story so I won't bore you with the background info again.

Anyway I get a surge at idle that is strange, mostly when I am sitting at a traffic light or stopped with my foot on the break. The engine will suddenly jump up 200-300rpm causing the vehicle to surge forward, it happens frequently when stopped as described above, maybe every 2 minutes or so.

I also experience a low idle (500rpm in Drive) that I have not been able to cure not matter what I have done, plugs wires etc. The idle sounds and feels weak to as if the mixture is to rich.

Last week when I put on a new TPS sensor, I put it on incorrectly and it was not functioning, this caused the computer to throw 4 codes. Bank 1 lean, Bank 3 lean, huge Vacuum leak and another code I forgot.

I can understand the lean codes, as the engine would have no way of knowing the throttle position and the fuel trim would be screwed up, but could the failing TPS sensor also through the code for a Vacuum leak?

Maybe there was another code stored in the CEL as well.

Thanks for any help...

 

[ma96782]

the code for a Vacuum leak?

You KNOW that you could, just hook up a vacuum tester, to test for a leak.

Aloha, Mark

 

[NHale623]

Is your defroster on when the surge occurs?

 

[Lazzman]

Well does the heater count? I think sometimes it is, but I will have to watch it more closely.

I did have the intake smoked with fog to check for leaks but there were none, is that the same effect as testing with a vacuum gauge?

Thanks

 

[Turdle]

OK
Did you get a good tps idle voltage??
What is it?

 

[NHale623]

Well does the heater count?

It might. Here's the reason I ask about the defrost....

When you select defrost, the A/C compressor will cycle to aid in removing moisture. When the A/C compressor cycles on, it sends a signal to the PCM for the additional load and the PCM will respond.

I know with my truck, at idle, it will definitely surge at idle when the compressor cycles on. Some of that may be due to an old IAC valve. Mine tends to stick so when it finally decides to move, you'll feel it.

Is your TPS currently functioning properly now, and do you have any codes?

 

[Lazzman]

Yes the TPS is functioning correctly now and I have no Codes.

I was so frustrated with the repair this weekend, breaking the new motorcraft TPS and all that I just put it on and did not get the Voltage.

I think the IAC may be a clunker, its from NAPA but is less than a year old.

Funny thing though when the TPS was malfunctioning the engine had no problem revving to 1500rpm when in Park and 1100rpm when in Drive, so I guess that means the IAC is able to function, right?

I don't recall having the defrost on often and the motor still surges. The weak idle is a concern, even with the hood up and motor running you can see tiny misfires that shudder the engine a bit. I know that a proper running engine sits dead solid with no shake in the engine bay.

Could it be the IAC Valve? I cleaned it really good a couple of months back. Even when I replaced it last February the idle was no different than with the old one installed.

 

[aldive]

I know that a proper running engine sits dead solid with no shake in the engine bay.
.

Not a V6.

 

[aldive]

I was so frustrated with the repair this weekend, breaking the new motorcraft TPS and all that I just put it on and did not get the Voltage.

There is no need to do that. The computer will make any needed adjustments.

I have never fooled with mine and have never had any issues.

 

[Turdle]

OK
Did you get a good tps idle voltage??
What is it?

If you have it set to .96--I suggest .89---

try it!!!

 

[NHale623]

I know that a proper running engine sits dead solid with no shake in the engine bay.

To echo what Al said, this is absolutely not true. Neither my Explorer, Model A, or wife's Windstar will idle without vibration or movement.

In that your problem appeared to go away with the new TPS, I wouldn't jump to the conclusion the IAC is bad. Mine surges because it sticks and is slow to respond (especially when it is cold).

I think you need to get a scanner and see what the PCM is seeing.

 

[aldive]

I think you need to get a scanner and see what the PCM is seeing.

Indeed; I have been telling him that forever.

 

[Lazzman]

True al, very true but I don't have the $350 to plunk down on a scanner, then again I would save on repair shop miss Diagnoses.

I know al like you do that a scanner has always been my best option, I am just reluctant to purchase one.

Thanks for the info about the V6's shaking a bit. Youre right the engines I have seen sitting steady have been mild V8's.

 

[Jakee]

True al, very true but I don't have the $350 to plunk down on a scanner, then again I would save on repair shop miss Diagnoses.

I know al like you do that a scanner has always been my best option, I am just reluctant to purchase one.

Thanks for the info about the V6's shaking a bit. Youre right the engines I have seen sitting steady have been mild V8's.

You'll actually save money not replacing things that are good.


And to make this interesting, my V6 hardly shakes!

 

[Charlie Brown]

Engine Stumbling & Lack of Power

Ocassionally, while stopped at a light, the engines stumbles and rpm lowers.
Right after that, while accelerating the vehicle seems to lack power. After
taking foot off accelerator then re-applying, engine seems to pickup speed.
These symptoms are intermittent, but seems to happen at every driving
interval. Not sure if it is a ignition problem, vacuum leak, or transmission problem. I've changed the spark plugs, wires, gas filter. Also drained, filled &
changed the transmission fluid. Nothing seems to have changed the results.
99 XLT.