real rough idle

[dajuiceman]

so today after I filled up with some mobil gas my car started acting wierd (i did check my gas cap). It runs fine but when I come to a stop and when it's just idling it acts real rough, even to the point where my car is rocking back and fourth a little bit. once I hit the accelerator again then my car is fine. My check engine light is on right now so i'll get it checked tomorrow. Also whats wierd is after I went to the store and I started my car my ses light was gone and it was idling normal again. But after I left again to get my son the light came back and it was acting stupid again.

[rixGAphx]

'99 V6, 8-yrs old, so about 100k miles?
Is the SES light flashing, or solid?
Solid = Minor problem that needs attention within a few days to a week.
Flashing = Major problem that will soon destroy the catalytic converter and other stuff like teh O2 sensor.

The 'filling up with gas' seems to have been a coincidence.

*Most* problems of 'rough-idle/fine-running' are caused by a vacuum leak, but they will rarely cause an SES light.
Loose gas cap will cause the SES light, but won't cause any running or idle problems.

Your car was due for MAJOR service at about 90k miles, including changing plugs, wires, fuel filter, and tranny fluid, and checking air filter and all sensors.
Your engine mounts should also be checked, since they DO fail and will then magnify the vibrations of engine roughness.
Have you had this major service, or something similar?

Smell your exhaust: Is there an odor of raw, unburned gasoline?

Let us know the code(s) that are scanned and we'll try to help.
Personally, I'm thinking the Fuel Pressure Regulator has failed, allowing too much pressure behind the injectors and therefore causing a rich mixture.
The O2 sensor and the PCM are reducing the richness somewhat when the throttle is being used (driving), but it's still so rich that a code is being set (for misfire, P030x); at idle, the 'puter is just running at preset values and causing extreme richness.

Hope this helps,
-Rick

[slowbird]

^^ :agree:

There is still a chance that it's bad gas...but what Rick has suggested is much more likely.

[dajuiceman]

I just got back from getting my codes checked. Apparently the computer that auto zone had said it is my egr valve. From what I have heard in the past (maybe you guys can confirm this) is that you can clean the egr valve first because carbon can deposit in there and if cleaning it doenst fix the problem then you need to buy a new one. I did my spark plugs and wires and fuel filter last year as well as a transmission flud change (of course my oil and oil filter and air filter are changed regularly). I'm thinking about buying some new 02 sensors because I dont know if these have been changed and it should help my gas milage some.

(oh yeah, the ses light is solid)

[GarciaNY]

sounds kinda crazy...

but check and see if all visible wires are fully plugged in...

its the reason myne wasnt runnin good

[slowbird]

I cleaned the EGR for my old 3.1L MPFI Sunbird...but not the ones for these newer motors.

...and yes, Changing the Front O2 on the Exhaust manifold will help with power/fuel economy.

The rear one has no effect on performance/Fuel economy whatsoever. Don't change it.

[dajuiceman]

interesting, didnt know that about the rear o2 sensor. Whats the purpose for the rear o2 sensor if it doesnt affect performance or gas mileage. also if the rear one goes bad will it trigger the ses light.

[slowbird]

Originally posted by dajuiceman
interesting, didnt know that about the rear o2 sensor. Whats the purpose for the rear o2 sensor if it doesnt affect performance or gas mileage. also if the rear one goes bad will it trigger the ses light.

The rear O2 measure the exhaust exiting the Catalytic. If it measures a reading that isn't normal it will throw a rear O2 code.

It's there to let you know when your Cat is failing.

Sometimes when people add a Highflow cat it will set the rear O2 sensor off and throw a Code.

[pokesmot]

So by the sounds of it the pintle valve inside the EGR jammed open slighlty (probably got caked with carbon) causing excessive amounts of exhaust to get drawn into the intake; causing your car to run like crap!

You should be able to clean the EGR and try and unjam the pintle; I've seen it done before on 3800's and old 3100's.

I recommend a can of SeaFoam; remove the EGR and spray everything as best as possible. You will need a new egr gasket.

before you disassemble the EGR, remove it first and examine the pintle's check to see if they are in fact stuck open.

[dajuiceman]

dont ask me how but somehow my car fixed itself. I had to go get sleeping pills and my car started and idled normal but the light was still on. I turned my car off to go into the store and when I came out and started it, it was idleing normal and my ses light went away.

[rixGAphx]

Originally posted by dajuiceman
dont ask me how but somehow my car fixed itself. I had to go get sleeping pills and my car started and idled normal but the light was still on. I turned my car off to go into the store and when I came out and started it, it was idleing normal and my ses light went away. EGR valves often do that.
Temporarily.

The problem will return.
Meantime, more and more crud is building-up in the passages leading to/from the valve itself.

'Twould be easiest to remove the valve now and clean it and its passages, before that $300 part is ruined.

[pokesmot]

Originally posted by rixGAphx
EGR valves often do that.
Temporarily.

The problem will return.
Meantime, more and more crud is building-up in the passages leading to/from the valve itself.

'Twould be easiest to remove the valve now and clean it and its passages, before that $300 part is ruined.

^ :agree:

I've seen special EGR gaskets that have a mesh screen built into them to help protect the EGR valve from accumulating carbon deposits; instead of clogging the EGR, it just clogs up the screen on the gasket instead.