Good afternoon all, have a 2002 SL2 1.9, 153k miles, great car. It is surging on acceleration, after warm up. I replaced the temperature sensor that is near the EGR, made an EGR blockoff plate and installed it, disconnected the EGR. Took the air inlet apart and cleaned up the backside of the butterfly (it was gummed up something horrid). Cleaned up around the idle air control as well, that was pretty gummy. Ordering a new fuel filter for good measure, but it runs strong cold so I don't think that's the culprit. The only code it has is for the EGR.

Anyone have any advice as to what to check next? Do not want to throw parts at it...

Thanks in advance,

Doc

 

What are the RPMs at cold start?

What are the RPMs when fully at operating temperature? Does the RPM wander at idle or is it pretty steady plus minus 10?

Automatic or manual? Sorry if it is in your description but I cannot see the post right now

Can you please elaborate on surging at acceleration? Does this mean at a constant throttle position that the RPMs and the actual output of the engine are slightly increasing then returning slightly increasing then returning? Different people describe things differently so I want to make sure I understand the symptom.

What happens to the RPMs if you are driving at constant throttle position and remove your foot from the gas pedal without touching the brake?

What's the new ECTS, does the cooling fan come on properly as the temperature gauge which is somewhere between 1/2 and 3/4 on the dash?

Which EGR code were you getting before he removed the EGR? This is likely important because it tells you what the PCM sees as incorrect operation. Meaning stuck open versus stuck closed versus insufficient EGR flow insufficient, EGR valve insufficient travel.,. I believe the adjustments made by the PCM are different for different EGR errors due to how the errors effect how much exhaust gas is recirculated.

Sorry for the boat load of questions but the more I have to work with, the easier this will likely be to solve. Happy to know others are out there that are smart enough not to shotgun parts.......
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You can block off the EGR an OBD2 car for testing purposes but I believe the PCM will always try to adjust for the malfunction even if the valve itself is not present. I think.
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Please post answers all from the same drive of the car so that everything is on an even keel or shall I say same reference.

 

RPMs at cold start are normal, I will pay attention to the RPM's this morning when I start for work, but nothing out of the ordinary there.

Surging is sudden lack of power momentarily when accelerating or during constant throttle position, can sometimes be alleviated my quickly moving the gas pedal. It "surges" to lack of power rather than extra power, so surging is not a good description, is it, more of quick power fall off.

It is a manual trans, so if I take my foot off the gas without touching the brake it just deaccelerates. The engine seems fine then.

The original codes were 404 and 1404, I have those on a note here somewhere, and will validate them today.

I do not mind the questions, if it helps me get the car running right again!! Love this little car....

The throttle plate was really gummed up. Got me to thinking, there are two vacuum ports on top of the throttle assembly. Could the area/device that those vacuum lines lead to be gummed up with the same sticky crap that was on the backside of the butterfly?

Thanks for helping!

Doc

 

Both those codes deal with EGR open performance. One says that the pintle is not opening to the location that the PCM says it should, the other one says it is stuck open entirely.

If you have never pulled and cleaned the EGR valve, now sounds like a good time. However, measure the resistance between the center pin and each side pin As you move the pintle up and down. What do you find?

Also, where did you source the new ects from? What's the one you removed resin tipped or all brass? Did you also replace the connector on the pigtail for it?

Is the hesitation at the same RPM regardless of what gear you are in?

was this a sudden onset condition or did it gradually get worse and then throw EGR codes?

 

I agree with derf about pulling the EGR and cleaning it. You'll also need to get as much carbon as possible out of the port where it's bolted on. If the pintle is stuck, you might be able to free it up with some carburetor cleaner and light tapping on a wooden block. Don't use a hammer as you could damage the point and it won't seal.

 

All right... found all of the codes that it had originally. P341, P404, P1404, and P1404P. After I cleared it the P341 has not returned. This started gradually, though I'm not entirely sure, it was the wife's car, but I re-inherited it again when I got her a new(er) Traverse.

Should it try to work with the EGR with it blocked off entirely? I hoped that blocking (with a blockout plate) would remove it from the equation entirely. I've tried it with the EGR blockout, and the EGR connected, and disconnected, seems the same. Guess it makes sense that it may be "compensating" even with the EGR blocked.

The old temp sensor was brass tipped. Saw it when I removed it, but it was out so I just put the new one (from Autozone) in anyway. I did not remove and replace the pigtail for the temp sensor.

The hesitation is in all gears, RPM's at idle are about 1200, it was doing that idle ok, then drop way down and run rough, and I thought cleaning that idle control on the intake may help that. It was really gummed up, like the butterfly, but the carb cleaner worked well on it. On the way to work today it did not drop and idle rough again...

Looked at replacement EGR valves, why the heck are they so $$$, and are the less $$$ ones ok?

 

1) Always use throttle body cleaner, not carb cleaner, on the throttle body. Carb cleaner dissolves the protective coating on it.

[Novel]
P0341 is an ignition related code. Hasn't come back so we'll assume a one off for now..

P1404 P is a pending 1404 and we covered p0404 above.

Usually the hesitation associated with a bad ECTS on an S car is more of a hesitating stumble but not with any huge loss of power.

If your RPMs are taking a dive when you accelerate, it does sound like an EGR issue. I have found these issues tend to show up on acceleration or deceleration depending on the cause.

The air to fuel ratio when the EGR is open takes into account how much air should be coming through the EGR. If the EGR valve is not where it's supposed to be, the amount of air or should I say exhaust mixed back in to the intake is not correct and throws off the air-fuel mixture.

If the EGR seems to be stuck open, that would be consistent with feeding too much of the exhaust with unburned gases back through to the intake.

Too much air per unit fuel because too much exhaust gas is being recirculated which would make the car run lean.

The harder you accelerate from idle the higher percentage of the time the e g r valve should stay open. But if yours is stuck open then it is letting the maximum amount of exhaust gas back through to the intake. More than is accounted for by the PCM.
So I believe you are leaning out as you accelerate and therefore starving the engine of gas and therefore losing power.
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Try cleaning the EGR by turning it upside down and filling it with carb cleaner. Let it sit for a few hours then rinse out. You will find splotches of carbon seemingly glued to this channels but with the right shaped tools, you can scrape most of it off without damaging anything. Do not bend the pintle or it will never seal and it is done for. Be sure to rotate the pinto with a screwdriver while cleaning it and to press it in and out until it moves freely.

If this is the original EGR on the vehicle with that mileage on it, you may not be able to get it clean enough to function properly. But definitely try. I have read on other forums that people use brake cleaner. Seems kind of harsh as there are seals inside but your choice. Pay special attention to what I call the cross channels between the two sections of the valve.

Now you are half done.

You need to remove as much carbon buildup in the tube running to the intake Port of the EGR valve. Rest the EGR valve on the mounting flange and you can figure out from the piping which is the input and which is the output, remembering that the input to the valve is exhaust.

Spray a healthy amount of carb cleaner down the inside walls of that pipe. Keep in mind that the carb cleaner is flammable so don't spray 3/4 of a can down in there and make a bomb. Put on some ear protection, cover the output of that tube with a bunch of rags or hold a bunch of rags over it while someone else cranks and runs the engine. Once it starts you will get a blast of half dissolved carbon slime. If you don't cover the end of that pipe, it will be distributed onto whatever is in front of the car as well as all over the engine bay. Revving the engine up to 3000 RPM a few times should blast a lot of the carbon crap out of there. No need to run the engine for very long as you are running it with absolutely no sound deadening. You are listening to raw exhaust coming out of the manifold and it is effing loud. Turn off the car, clean up the mess, and repeat until you are satisfied.

If you don't clean this pipe, the same exact EGR clog will form again so there's no point or cleaning the valve if you don't clean what feeds it.

Chances are you will not get the EGR clean enough on your first attempt if you have never done this before. Do not be discouraged. Pull the valve again and repeat cleaning and careful scraping cycle. you just need to make sure that the pintle moves freely and that the gap between the pintle and the bore is uniformly clean.

Enjoy.

[/Novel]

 

I will clean it, but it is currently blocked out with an aluminum blockout plate that I made, with a gasket on each side. Does that factor into this at all? I am trying to understand if the computer thinks there is something still "wrong" in the EGR system and it's compensating by making the car surge.

I appreciate your inputs and experience...

Doc

 

Having just reviewed all of the posts, do you mean the car idles at 1200 RPM when warmed at operating temperature or 1200 RPM when started?

If it idles at 1200 RPM at operating temperature you likely have a vacuum leak somewhere that is letting unmetered air get to the intake and leaning out the mixture.
I do not doubt that your EGR valve is clogged and sticking. However my manual transmission 97 SC2 idles at 850 RPM and I believe the automatics are somewhere around 750 RPM.

I believe the m a p sensor will compensate for the meter to air difference with and without the EGR, but it cannot compensate for unmetered air which it does not sense. The s series cars used map sensors not mafs.

So my statement before about the PCM trying to adjust for the absence of the exhaust gas usually recirculated through the EGR wasn't quite right. It's actually the map sensor input to the PCM that allows it to determine the correct air to fuel mixture, along with other input factors.

The reasoning in this post does explain why you still have the issue even with the EGR blocked off. 1200 RPM at operating temperature is way too high. The car stumbles below that likely because there is too much unmetered air sneaking in and thinning out the mixture.

Did you remove the entire throttle body? If you did and did not replace the gasket with a new one, that may be the source. I know you were having the issue before you ever touched anything but you said it was gradual so what is possible that gasket was already leaking. We will never know.

In general you can check for vacuum leaks buy spraying carb cleaner around the ends of vacuum hoses actually the entire hose where they connect different parts of the engine. Other popular places for leaks on S cars are the throttle body gasket and the intake manifold gasket. If you hear the RPMs increase when spraying in a particular area , you have located a vacuum leak.

Apologies for missing the 1200 answer earlier. However everything I posted about the EGR needs to be done as well to get rid of the EGR codes and the strangeness that comes with a malfunctioning EGR.

 

Hey, Good Morning, I should clarify the 1200 RPM idle is a cold idle, when warmed up it idles at 750-800, that part seems normal. I did remove the entire throttle body, the gasket seemed fine, but I will probably get another. One of those deals where I took it off to see how difficult it was, and it wasn't difficult, and the throttle body was so gummed up it was sticking... I used carb cleaner, but that is water under the bridge.

I noticed yesterday that it doesn't surge/stumble when cold. As soon as the temp moves off the peg it will stumble thought. After warmed up, at WOT it runs out well. Yesterday on the way home I risked a ticket and ran it out through the gears, and getting on it the engine pulled fine. Well, as least as fine as a 1.9 mileage getter Saturn will run out... Surprised the Subaru beside me though. Anyway...

Oddly enough, the engine codes cleared yesterday too. Still the stumble/surge though.

Thoughts on O2 sensor? TPS? How to test each?

Anyway, hope my observations shed a bit more light on this. I am ordering a gas filter for it for good measure (Autozone doesn't have one, Amazon does), and ready to do any more troubleshooting you may suggest. The weather is warmer here so it's much easier to get out and work outside. Garage is full of my son's hotrod build...

Thanks for your suggestions/thoughts!