Hello everyone, I am new to this forum as of yesterday. I was hoping people could help me with an issue I was having.

My 1999 SL2 has been idling inconsistently for the past several months. Most of the time it is fine, but sometimes it idles really high when I put it in park and other times it doesn't want to idle. It has tried to die on me when at a few stop lights. I can keep it alive as long as I have the accelerator depressed. The "Service Engine Soon" light turned on on our last encounter. I decided it was time to do something about it. I went out and bought a nice little Craftsman On Board Diagnostics Reader (since it costs $130 for a mechanic to do it out here) and when I checked her out, it gave me two codes:

P0108 - Manifold Absolute Pressure/BARO Sensor High Input
P0404 - Exhaust Gas Recirculation Control Circuit Range/Performance

I found the following links to these two issues:

http://www.obd-codes.com/p0108
http://www.obd-codes.com/p0404

What do you guys think? Idle Air Control Valve? EGR Valve? Clean the throttle body? O2 Sensor?

EGR Valves are kinda expensive so if I can just clean it first I would prefer to do that.

Also, the guy who sold me the car never told me that the engine had either a cracked block or a blown head gasket. The car has actually run quite well the past year and a half even with this trip up but it does smoke slightly and I do have to top it off with oil every month or so. At first I was thinking this issue was a problem with a loss in cylinder compression but I don't think so anymore. Any help would be appreciated. I will get to working on it this coming weekend. Thanks.

Stephen

 

I'd pull the EGR and clean it first if it were mine. The pintle can get a carbon build up on it and stick. Be sure to take a stiff wire and clear the passage on the intake too. Use a new EGR gasket if you can find one. If that doesn't seem to solve it, get a can of throttle body cleaner and clean it. As far as using oil, if you have the 1.0 DOHC engine, they're notorious for that. Go to a 10w-40 weight oil and that will help. What color is the smoke coming out of the tail pipe? If it's not white and has a sweet smell to it, it's most likely not a water leak into the cylinders. It could be related to a faulty EGR valve or even an O2 sensor.

 

throttle body and egr cleaning for starters.
I use carb/choke cleaner to clean egr and throttle body cleaner for the throttle body.
.
Be sure that you do not damage the EGR pintle (center part that moves) during cleaning.

 

Also check for an intake manifold gasket leak around the #1 cylinder. It will cause all the symptoms except the P0108.

 

The p108 may not be the cause of a problem but the result of one. If the engine is popping back through the intake with sort of a back fire type thing that can cause a p108 to be read.

Should that be true, the back fire could be in part caused by the EGR valve giving problems. It sounds to me as if cleaning things is a good place to start.
EGR problems can and have been caused by getting dirty. And while you are there cleaning things, the throttle body has been known to be pretty cruddy too causing drive ability and idle problems.

 

Thank you for all the information! I did pick up a can of throttle body cleaner so I will get at it this weekend.

Rubeyahseed - The smoke is more of a light gray color. It is definitely not a white color. It doesn't billow out but when the car has been running for a long time it starts to get worse. Inside my coolant reservoir are tiny black rubber specs. However, the coolant level stays consistent. It's the oil level that I have to watch. I guess I had always been under the assumption that for that type of problem, I would want a more viscous oil, like 20-50W. Is this too thick? You say 10-40 would be better?

Keith - Is there anyway to check for a leak besides pulling the intake manifold?

 

Spray carb cleaner or the something like it around the intake where it meets the head while the car is running. Listen for idle changes

 

Until somebody in marketing determined that people would flock to the show room and buy the car with best gas mileage, thus recomending the lightest weight oil that could possibly be purchased and still have the engine last long enough to get through the warranty with out wearing itself out. People used the best oil weight based on how it affected wear on the engine for winter and summer. Or as multi-viscosity oils got better picked one that best represented the weight that would again protect the engine yet would work well in all seasons.

The first number in a multi-viscosity oil such as the 5 in 5w20 pretty much means if you live real close to the north pole, it is a good weight. The 20 pretty much says if you live in Southern Canada the temperature there in the summer might require it.
But if you live where it gets hot in th summer and some where around freezing in the winter, 5W20 might just wear the engine out. But who cares? the warranty is up.
Not the factories problem.
This is known as reading the oil viscosity vs temperature chart and then selecting an appropriate oil.
10W40 is far better than 5W20. The temperature range covered is pretty much universal across the U.S.
I live in Phoenix AZ. It is 42 degrees right now and with in 5 degrees of just about as cold as it gets any time.
During the summer 120 can be seen although 115 is seen more often.
I use 20W50 in all of my cars, year around and from the day they come off the show room floor.
The engines do not wear out, nor do they consume oil. My Saturn, purchased in 1996 does not consume oil after well over 100,000 miles. It is a good oil viscosity for my temperature zone.
If I could not find 20W50 I would use 10 or 15W40. In fact I use Mobile 1 in my Chrysler and it is a 15W50
So the best viscosity is the one that is best suited for your temperature zone and 5W20 is not suited for any one living in the US's temperature zone. Us it and the long term affect is engine wear and oil consumption.

 

I just bought Castrol Syntec 10w-40 for my Grand Caravan yesterday and picked up some Mobil One 10w-30 for my Equinox. I was hoping to change the oil in both today, but it's raining, so it'll have to wait.

 

As sw2cam said, you can spray some carburetor cleaner or throttle body cleaner around the gasket. You can also use wd40 or any number of things, if the manifold gasket is leaking, your idle will change. What changes will be determined by what you are using, but something will change.

The problem area is around the #1 cylinder because the gasket is not well supported in this area. There is no bridge on the head side between the #1 and #2 ports and there are only three bolts around this port leaving a full 180° without any clamping pressure. All the other ports have 4 bolts around them.

If you do have a leaking gasket, use a felpro replacement, do not use another factory gasket. The felpro has a metal layer and doesn't get pulled in as easily as the all fabric factory gasket.