Idle problems

[davr333]

I have a 94 mtx that has been having idle issues. The car also has a sho shop supercharger kit on it. It started off with the idle jumping only one or two hundred rpms for a couple times and then it started to jump from about 500 to 1500. I have not been driving it, but when I took it around the block it seemed fine in gear and as soon as you put it back in neutral it starts bouncing. I have checked the codes a couple of times and the only codes that have come up were the MAF code(157) and after that was an oxygen sensor code(173). There was also a 511 code, but from what I read that was normal if you have a chip installed. I have changed out the vacuum lines, IAT, and TPS. The MAF has also been cleaned and just recently changed the oxygen sensors. After changing all these part now the car will idle fine for the first couple minutes then it will start acting up again and no other codes. I am going to try a cylinder balance test tomorrow. Any help or suggestions would be appreciated.
Thanks

 

[jmpSHO]

Sometimes cleaning the MAF doesn't fix it, it might need to be replaced.

 

[davr333]

Thanks for the response. I had a small idle problem in summer, that got better after cleaning the MAF . Maybe the sensor just went bad. I just ordered one last night.

 

[maverick218]

my car was kinda doing that for awhile and i changed the DIS that helped out.

 

[davr333]

I just finished trying another MAF and nothing changed. I guess I will try replacing the DIS tomorrow. Thanks

 

[needaQuaife]

mine stumbles sometimes when cold, then after she warms up, idles perfectly.?

 

[davr333]

The car idles ok when first started because of it being around 1500rpm, but when it comes back down to the 1000rpm it starts to jump. If you give it gas and hold the rpm around 1800rpm or more it seems fine. When you let off the gas the tac drops to about 600rpm and continues to jump. Tried another DIS and still acting about the same. The way it was acting I though it would be a vacuum leak. Probably going to remove the intake and put it back together.

 

[davr333]

I recently check the fuel pressure on the car and when the engine was off and the key in the on position, the pressure was at 8psi. After that when the car was turned on the fuel pressure was at about 56psi and a little fluid(think it was gas) was coming out of the muffler. I was looking at some posts and the fuel pressure should be in the 35psi range and it sounds like the fpr is bad. I was just looking for any other opinions if this is the problem.
Thanks

 

[dondo_sho]

is the IAT you list above the idle air control valve?
It was causing my car to jump around at idle and when cold. it would hold rpms from 2k-3k after releasing the throttle. It would slowly comeback down to 1k.

I let the computer relearn how to idle by: disconnecting the battery for about 10 min. Started the car and turned on all accesorries. The idle was still erratic. I replaced the idle air control valve with a JY part. and it has been fine ever since.

 

[jon93]

I recently check the fuel pressure on the car and when the engine was off and the key in the on position, the pressure was at 8psi. After that when the car was turned on the fuel pressure was at about 56psi and a little fluid(think it was gas) was coming out of the muffler. I was looking at some posts and the fuel pressure should be in the 35psi range and it sounds like the fpr is bad. I was just looking for any other opinions if this is the problem.
Thanks

Your car most likely needs a new tune (shoshop tune is crap), an aftermarket fuel pressure regulator, and a better Mass Airflow Sensor.

 

[davr333]

I recently put in a sho nut fpr and it is better, but still probably needs a tune and may have a small vac leak. I have a tweecer rt and just need to get the wide band installed before I try to tune it.

 

[catdaddy]

Sorry to thread steal, don't know how to start a thread. I have a '95 ATX with the 3.2. Hard as he!! to get it started with a lot of popping in the intake. My neighbor tapped on the 2 vaccum diaphram pots that are attached to the fuel rail and it would run and idle a little better. He said they are the fuel pressure regulator. Is that right? The car will not idle on its own til it gets warmed up and then it's a rough idle. The check engine light comes on intermittantly but I don't know how to check the codes. Can y'all help a poor idiot out?

 

[davr333]

The fuel pressure regulator is the one with the vacuum line on top. As for the codes, this site should help http://www.shophoenixproject.com/eec/eec.htm. Make sure to check the stored codes like it mentions.

 

[catdaddy]

The fuel pressure regulator is the one with the vacuum line on top. As for the codes, this site should help http://www.shophoenixproject.com/eec/eec.htm. Make sure to check the stored codes like it mentions.

Thank you very much!