1995 Astro rough idle after warm up..any ideas?

[tittymonster]

1995 4.3 v6 160000 miles runs good for about 3 minuets then starts to sputter's and miss eventiualy stalls...

I changed the cap,rotor,fuel filter,even the altinator thinking it was due to low voltage...the check engine light is NOT on,no codes

I ran it in a dark garage, NO sparks from the plug wires to ground...
Im getting ready to give it a bullet

[tittymonster]

Since I got no replies, I tried removing the ERG valve, cleaned it and reinstalled it...no help

also went to the junk yard and tried swapping out the ignition module and map sensor...same problem..rough idle after warm up...

Has anyone fixed this problem? could it be the O2 sensor???
the check engine light is still OFF, no codes stored just reads 12 over and over

ANYONE HAVE AN IDEA? ANYONE AT ALL...

[billmanure]

I have a 95 with the same problem. Problem is, it about last on the list of 4 or5 things that need fixing. I wish I could help, but I will watch this thread for info from someone that knows.

[AustinAstroGuy]

You might want to check for vacuum leaks.

There are several vacuum hoses that run inside of a wire harness that is located between the vehicle battery and the firewall. They are hard plastic vacuum lines usually black in color and not much bigger than the electrical wires in the same harness. For some reason, the insulation on the electrical wires will eat through the plastic vacuum lines which causes vacuum leaks. You have to remove the battery and remove the tape from the wire harness to find the problem. I think there are at least three vacuum lines in this harness. I had holes in two of the vacuum lines. If you find a break, you may be able to splice with some rubber tubing and silicon sealant.

In addition to making the van run very poorly, I also noticed vent air always coming out of my defroster ducts even with defroster off. One of the broken vacuum lines was preventing the defroster vent from closing.

I read about this problem elsewhere in these forums and was very greatfull that someone had figured this out and took the time to post it.

Hope this helps.

[tittymonster]

thanks, Ill try anything to get it running

[old_master]

The time frame of 3 minutes is approximately when the PCM goes into closed loop. More than likely the problem is computer related. While the engine is warming up, it operates in what is called open loop. During open loop the PCM ignores the oxygen sensors while they warm up too. When the oxygen sensors reach operating temperature, they create a voltage anywhere from .1 to .9 volts depending on fuel mixture. When the system switches to closed loop, provided the sensors are within range, they will not set a DTC, (Diagnostic Trouble Code). If the sensors are slow to react to changes in fuel mixture, the engine will run poorly and not necessarily set a DTC. The factory recommends replacing the oxygen sensors at 100,000 miles. Usually by that time the sensors reaction time slows to the point that is causes poor performance and poor fuel mileage. If your O2 sensors have not been replaced yet, they're due.

[tittymonster]

Thanks for the info...I unplugged the O2 sensor and it runs now without the idle problem and without tripping the Check Engine Light...Now the big question...is it a bad O2 sensor or is the computer shot..I thought the CEL would come on if the O2 sensor was unplugged..

[old_master]

If the sensor is unplugged, the SES light should come on, it may not come on right away though. How many oxygen sensors are on your vehicle? How many wires at each sensor? The PCM is a substantial part and rarely has problems.

[tittymonster]

I found only one just above (motor side) of the CAT CONVERT under the passanger seat...it has three wires on it..I let it idle for about 15 Min's and it seems ok..A little knock if I rev it up..I think the timing might be a little off..I could have knocked it off when I put the cap on, it seemed lose...I lined up the makes and tightened it down, but it may be off a little..

Gas just hit $3.19 here so Im going to sell it..I went and got a Escort (yuck) wagon that gets 28mpg around town..It might be the lesser of two evils..