98 Lesabre engine idle not steady on occasion

[swipter]

On my 98 Lesabre the engine idle is unsteady at times. On occasion the engine will cut off. I have scanned it for codes and there are none. Can anyone tell me what may cause this?

[avatar307]

Have you tried replacing the fuel filter?

Have you checked all your vacuum lines for cracks, holes, degradation?

When was the last time you replaced the spark plugs?

[swipter]

The plugs and wires are new. I didn't realize there were vacuum lines on there. WHere would they be. THe fuel filter has about 30k on it. Is it time to do that also?

[avatar307]

It's not necessarily "time" to change the fuel filter. According to Buick, they are supposed to last the life of the car. However, if you're gas tank got some rust in it or if you've been using dirty fuel, it may be clogged up after only 30k miles.

I could see a fuel filter causing symptoms like these, but you'd just as well check the vacuum hoses before you got spend $10 on one. The vacuum lines will all come out of the vacuum manifold, which comes out the top of the intake manifold.

Probably the easiest way to find it is to spot the large hose coming out of the brake master cylinder, on the left of the brake fluid reservoir. Follow that large hose back (it's a vacuum line for the brakes), it connects to the upper most vacuum port. Under it you'll see several much smaller tubes coming out of both sides of the vacuum manifold.

My 1995 has 5 vacuum lines coming out. The large one for the brake system, which I've already noted. Below that, coming out towards the front are 2 U-shaped tubes that connect to hard PVC vacuum lines. One of these goes to the transmission modulator, and the other goes to the EVAP system. Out the back side, one vacuum hose goes to the fluid pressure regulator (has a gas line coming out of it), and the other one goes to a check valve. The check valve is little round thing that slits the vacuum to two other hoses, one to the cruise control and one to the interior environmental controls. (The check valve exists to prevent a vacuum leak in your cruise or environmental controls from depriving the other more critical components of vacuum.)

A leak in pretty well any of the vacuum lines will change the amount of vacuum available to the other components. One of which is you fuel pressure regulator. If you've got a bad vacuum line, the fuel pressure to the injectors could be too high or two low. Likewise, incorrect pressure to the EVAP canister could theoretically cause too much vacuum in the gas tank and inhibit fuel flow.

Anyway... pull somewhat firmly on each vacuum line. They should all stay put and not slip off. Visual inspect them for cracks or deterioration. Vacuum hose is cheap, might as well fix any problems with the hoses now and see if it helps.

[swipter]

So it sounds to me that a vacuum leak, intermittent, could cause the tranny to shift Erratically also. Could this be true? I will check and replace those lines this weekend. THanks for your help.

[sierrap615]

if you have a scantool with datastream access and freeze frame, use it, check all your sensor and also inspect the EGR and IAC, if ether of those are clogged, it will act like a vacuum leak, and could be intermittent

[swipter]

Can the EGR and the IAC be unplugged or do you have to buy new ones? By the way, what is an IAC?

[avatar307]

Nope, can't be unplugged. They are part of your emission control systems. If you unplug them, your service engine soon light with click on and your car will run like crap.

I believe IAC stands for Idle Air Control Valve. Which is an actuator that regulates the amount of air your car recieves at idle. I couldn't tell you where to find it on a Buick, I'm not sure if they have one.

[piewagn]

Pull the vacuum line off of the fuel pressure regulator. See if the inside is damp. I've seen these diaphrams go bad, which will cause fuel to be ingested into the intake via the vacuum line. This will cause erratic idle, and, stalling.

[swipter]

Where is the fuel pressure regulator found? I looked for the vacuum lines where you said. I guess I found them but they look like hard formed plastic with rubber elbows and connectors. If that is them, some of the rubber connectors are a bear to get off...I gave up.

[piewagn]

The fuel pressure regulator is attatched directly to the fuel rail. There is a plastic block on top of the throttle body with vacuum lines coming off of it. Follow the vaccuum line that goes toward the front of the vehicle.
The regulator is actually fairly close to the throttle body. The Schrader valve service port is at this same location.

[swipter]

Found it, thanks. No moisture in there.

[sierrap615]

the IAC is mounted inside the throttle body on 90% of car, it has two or four wires and is a solenoid with a pintle on the end hidden inside a passageway of the throttle body, to clean it remove the intake tubing, spray it with sensor-safe carb and choke cleaner, work the thottle plate by hand alittle, and spray again, then start the engine so all that gunk gets burned off. here is an example of a IAC off a Saturn S-Series - http://www.saturnfans.com/photos/sho...p/photo/15887/