3.1 L Rough Idle Problems...

[91LuminaEuro]

I've been having this problem for a while and my dad, and i really need some help guys. My original plans were to get rid of the car this summer and get something newer, well long story short, i've got two handicap parents, my dad is going to need a hip replacement this summer, and my mom..who knows but im gonna have to help my dad at his shop as much as possible and money is going to be even more tight that i have ever expected, so i need to get this thing running perfect so i can stop worrying about it.

Here are some details:

1991 Lumina Euro 2 Door.

3.1l Jasper Engine installed in 2005
-New Injectors, New Throttlebody
-New Plugs & Wires
-Prom & Computer replaced

Everything electrical has been changed & replaced, basically everything except the entire engine has been looked at or replaced.

Here is the problem,

-Sometimes when you start it, it will start, and then just die instantly, and you can do this several times before it will spit and sputter and then catch its breath and run, but runs really badly. If you give it some gas and bring the RPMS up it will somewhat even out, but even then it doesn't run great.

-With the A/C off, it idles a little low and kind of rough, if you turn the A/C on it will even out and run a little better.

-And every now and then if it starts the first time, the idle will jump sporadically all over the place, until you bring the RPMs up and it will again kind of even out

-Most of the time the idle is somewhat rough, not really bad but not what it should be..



So please...help...


Any/All suggestions are helpful, just dont tell me to replace the car...i have one possible option with replacing it but id rather get it running right....

I posted this over at w-body too, but im just trying to get all the help i can get with this thing...

[86FieroSEv6]

It would be interesting to see what the temp sensors are saying at startup with the key on and the engine off just before cranking it. Also, a fuel pressure volume test would be good as well as checking the fuel pressure regulator vacuum line for the presence of fuel, as in a blown regulator diaphragm.

[91LuminaEuro]

Never thought about the temp....however, the problems are mostly intermittent, with the idle only kinda rough most of the time, all other symptoms are intermittent...so if it were a blown diaphragm in the pressure regulator, i would assume it would be more of a persistent problem...

[86FieroSEv6]

True that. Have you double checked that all the grounds are in good shape? Including the batt. to fender and engine to body as well as the ECM grounds? And let us not forget the infamous cam sensor/harness rot that takes place when the LIM end seal starts to leak oil onto it.

[91LuminaEuro]

Yeah, i mean my dad and i have gone through everything we can think of....he's an experienced mechanic, so we're really at odds with this thing...

I'm hoping some one here can offer some insight into something we've over-looked or something bizzarre we've never dealt with..

We've been over all the electronic components and checked them and/or replaced them all..

There is no mechanical adjustments as far as lifters or anythign goes...and its intermittent and its so hard to pin-point the circumstances at which it occurs because i've never found anything that seems to cause it..its very random...

[86FieroSEv6]

Erratic crank sensors, fussy ignition modules, erratic throttle position sensors, I assume ya'll have checked those out too? Have you "tap tested" the ECM? That means lightly rapping on the ECM case with a screwdriver handle or similar tool while the car is running.

[91LuminaEuro]

Yes, we've tested all of these items, however while they were tested the car wasnt really acting up...

I have no way of re-creating the circumstances, because like i said..they seem so random...

[86FieroSEv6]

Are there any aftermarket alarms or auto-start units installed on this vehicle?