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Nitro_Alltrac
06-29-2015, 07:55 PM
Ok, I was out and about today and the on the way home some red neck in a 4WD Chevy had to pull up and gun it and take off. I should know better give my advanced age but this kind of pissed me off so I hit it. I was pulling and rolling up on him at about 13 psi when I felt a small shudder and the boost dropped off and it felt like I lost some power.

Now instead of idling at about around 1000 (where this car has always idled regardless of 2nd or 3rd gen electronics) it's idling at 600-700 and kind of rough. The vacuum is fluctuating as well where it is usually rock steady. It drives OK under cruise but if you step on it, even a little, it doesn't seem to have the power it should.

The temp and oil pressure are right where they've been running. I'm hoping it's something in the ignition or fuel system. The plugs have less than 2K miles on them. Once it cools down I guess I'll pull plugs and see what those look like.

So, what are the suggestions. At first thought does this look like something simple or a major fuck up? I'm just trying to narrow some things down and see if I can save some time diagnosing.

4thgenceli
06-29-2015, 09:51 PM
Vacuum leak?

Luni
06-29-2015, 10:30 PM
on Gen3 electronics, vacuum leak may cause it to actually idle high not low.

Nitro_Alltrac
07-02-2015, 03:05 AM
Well it finally quite raining long enough, and my disgust level dropped, and I popped the hood this evening to take a look. I think I might have found the problem. The vacuum line that feeds the MAP sensor from the manifold on my car is teed to the line that goes to the vacuum dashpot that has the stopper for the throttle linkage. (I know this isn't ideal but it's how the 2nd gen sensor was setup and I haven't taken time to find an individual source for it.)

Anyway, while I was looking over all the couplers and lines I found that the line going to that dashpot had come off. So, not only was the dashpot not working the MAP sensor would have been seeing enough, or maybe none at all, vacuum/pressure.

After I put it back on I started the car up and cold it idled right where it always does. I'm going to drive it to work tomorrow and see what it does. This makes some sense to me that if the MAP wasn't seeing the right vacuum/pressure signals it wouldn't be sending the right signals to the ECU for the correct amount of fuel. I guess I'll find out tomorrow.

Shadowlife25
07-02-2015, 10:06 AM
Awesome that it was something so simple, even if there were headaches getting to this point. :)

MCcelica
07-05-2015, 07:06 PM
It's always a relief when it is something simple, though.

Like when the 7th gen blew a brake line. If it actually had fluid in the system, you could see the hole in the brake line itself when it sprayed everywhere like a Windex bottle. Lol same thing, it's like, "I'm guessing that's where my problem is"

4thgenceli
07-06-2015, 03:03 AM
So it was a vacuum leak?

MCcelica
07-06-2015, 05:25 AM
So it was a vacuum leak?

Do you fucking read?

Luni
07-06-2015, 06:52 PM
I guess if the vac leak is on the sensor itself, it will cause it to idle low.

So there you go.

alltracman78
07-15-2015, 01:02 PM
on Gen3 electronics, vacuum leak may cause it to actually idle high not low.

Don't worry boss, you were right. :)
Vacuum leaks on a speed density [MAP] sensored system WILL cause it to idle high. If the leak is bad enough the idle will surge.
The exception being [as you found out :P] if the line to the MAP sensor itself is the problem.

Nitro_Alltrac
07-17-2015, 07:22 PM
Yeah, no vacuum signal to the MAP causes a few issue. LOL

Luni
07-25-2015, 06:54 AM
Don't worry boss, you were right. :)
Vacuum leaks on a speed density [MAP] sensored system WILL cause it to idle high. If the leak is bad enough the idle will surge.
The exception being [as you found out :P] if the line to the MAP sensor itself is the problem.

I just know what I had to deal with when I did my Gen3 EFI swap and working on other Gen3 cars with vac leaks. If the vac leak is on the manifold or in the throttle body NOT where the MAP is, it made it idle high every time. Glad to know Im not crazy :)

alltracman78
08-04-2015, 08:41 PM
Well, you are crazy.

Just not about this. :D