[markag]

Hi,

I've been fighting an acceleration issue with my car for a long time. Over the past couple of months, I've been repairing it trying to finally resolve the issue. So far, all the repairs I've made have offered improvement, but I still have the issue lingering there. I was hoping you guys may be able to help.

The issue I'm having is a lack of acceleration when the car warms up. When driving the car (starting from a stop, or accelerating from a constant speed) I will try to accelerate at a moderate to high rate. The car will pull hard for about 1/2 a second, and then it will bog down. When it bogs down, If I give it more gas it wont do anything. If I floor it, the car will downshift, but the car will be very harsh sounding, and the acceleration doesn't seem to match the rpm that the car is reaching. (the car's rpm will be in the 4000 range, but the acceleration only feels moderate). When the car starts to bog down, if I quickly release my foot from the gas and then quickly re-apply it to the same level it was just at, the car will start to accelerate as it should. No harshness, and no downshifting.

Like I said above, I've been making repairs to the car trying to alieveate this issue. It used to be a constant issue that was worse when the car reached operating temperature. Now it is an issue that only appears when the car reaches operating temp. Before it warms up, this car drives like I just pulled it off the showroom floor. Also, I'm not getting any check engine lights at all. I haven't had one throughout this entire process.

What I've done to is so far:
-Changed air filter
-Changed fuel filter
-Checked spark plugs, wires, coils (appeared fine, no arching or other issues)
-Replaced catalytic converter (was clogged, huge improvements in drivability)
-Tested for clogged muffler (not clogged)

I still want to check what the fuel pressure is at. It might be the fuel pump. Other then that though, maybe bad injectors and/or O2 sensors? I just don't know. I can say that each of the improvements listed above made a difference (except for the ones where I just checked things). My gas mileage has increased back what it was when I bought the car 5 or so years ago. The overall drivability has greatly improved, but this issue is still present whenever the car is warmed up. I would appreciate your help in tracking this down for good.

Thanks,
Markag

 

[Euthymia]

I'm not saying it is the automatic transmission system, but I am curious why you do not put it on your suspect list. After all, it would not light up the Check Engine, and you are getting pretty noticeable glitches with no engine light.

I know that checking the transmission fluid level is not a "user serviceable" feature on our vehicles, but since it sounds like it has some miles on it, how about taking it to a garage for a transmission fluid drain and refill?

My car is running pretty well, but I plan to take it for a drain and refill within the next few weeks just because it's a dozen years old.

Also see my posts in the Maintenance sub regarding cleaning the MAF sensor and throttle body. Those are relatively easy things that can also improve driveability (even if they don't cure your main issue).

 

[markag]

I'm not saying it is the automatic transmission system, but I am curious why you do not put it on your suspect list. After all, it would not light up the Check Engine, and you are getting pretty noticeable glitches with no engine light.

I know that checking the transmission fluid level is not a "user serviceable" feature on our vehicles, but since it sounds like it has some miles on it, how about taking it to a garage for a transmission fluid drain and refill?

My car is running pretty well, but I plan to take it for a drain and refill within the next few weeks just because it's a dozen years old.

Also see my posts in the Maintenance sub regarding cleaning the MAF sensor and throttle body. Those are relatively easy things that can also improve driveability (even if they don't cure your main issue).

I had initially suspeded the transmission as a possibility. I had spoke to someone I know who is a certified mechanic and he said it sounded more like an engine performance issue then a transmission issue. He gave me a list of things to check and to test on the car. I've basically worked through his list of items and that left me here. I have contacted him again, but I haven't heard back from him yet.

When I do have the acceleration issue though, it is more like my car is bogging down then my transmission is acting up or slipping. The weird harshness seems to come from when I try to force my car to accelerate by flooring it when it is in a state of being bogged down. I do agree that my transmission does have a lot of miles and probably isn't in the greatest shape, but I'm thinking that it isn't the cause of this issue in particular.

I should have mentioned in my first post that I did remove the air intake and cleaned the throttle body with it still attached to the manifold. I was suprised to find that when I pulled the air intake off that the throttle body and the MAF had absolutely no build up on them at all. They looked like new parts, that's how clean they were.

I'm starting to think now that it might be a bad EGR valve. I had been searching the internet for posts, videos, etc where people have had issues with acceleration once their car was warmed up. A youtube video turned up someone with an 04 Grand Am having very similar issues to mine. His problem ended up being caused by a bad EGR valve, and he simply unplugged it and his problem went away. Like me, he didn't have any check engine lights. I thought that sounded easy enough to try, so I unplugged the connector from my EGR valve this morning before I came to work. On my drive to work, my car did not have any issues with acceleration. It drove the same cold and warm. I want to drive it some more like this to see, but I think I may have tracked down the main culprit of my issues.

It makes sense to me that the EGR valve may have been the culprit because of the super clean throttle body and MAF sensor. In addition to that, a non functioning EGR would let the unburnt fuel from the engine go out the exhaust through the converter, potentially causing it to clog. The air and fuel filters needed to be changed just because it was their time, so general improvements were felt because of that. The only unusual part is that I did not get any check engine lights at all. I would have thought that the EGR would have triggered one. I haven't even got one now that I've completely unplugged the EGR. I'll just have to see what happens here as I continue to test it out.

 

[Euthymia]

....I unplugged the connector from my EGR valve this morning before I came to work. On my drive to work, my car did not have any issues with acceleration. It drove the same cold and warm. I want to drive it some more like this to see, but I think I may have tracked down the main culprit of my issues.

It makes sense to me that the EGR valve may have been the culprit because of the super clean throttle body and MAF sensor. In addition to that, a non functioning EGR would let the unburnt fuel from the engine go out the exhaust through the converter, potentially causing it to clog....The only unusual part is that I did not get any check engine lights at all. I would have thought that the EGR would have triggered one. I haven't even got one now that I've completely unplugged the EGR.

Woo-hoo! It does sound like you nailed it, and also caught something that would have eventually killed your new catalytic convertor.

Kinda weird that it doesn't make it throw a code. I thought the original main point of the Check Engine Light thing was to monitor emission-related stuff.

 

[markag]

Woo-hoo! It does sound like you nailed it, and also caught something that would have eventually killed your new catalytic convertor.

Kinda weird that it doesn't make it throw a code. I thought the original main point of the Check Engine Light thing was to monitor emission-related stuff.

I got a chance to drive the car more last night, and this definately seems to have fixed the issue. I'm no longer getting left in the dust at stoplights, the throttle response is much better, and I'm not getting any sort surgin/bogging any more. The other thing is I haven't had any of that harsh sounding high rpm acceleration any more. This definately seems like the issue.

As far as check engine lights go, the light did finally come on when I left work yesterday. I was expecting it to come on at some point since I completely disconnected the connector from the EGR valve. As far as the EGR potentially killing my cat. That is just a theory I have. I don't know if it can really do that or not, but it seems to make sense in my head

I'm just excited that I finally pinpointed the root cause of my problem. The other maintenance that I did was definetly worth the improvement too. All in all, I'll end up spending about $325 in total to fix the EGR, catalytic converter, air filter, & fuel filter. I'm sure if I had to take it in somewhere, I would be paying much more then that. The OEM converter alone probably would run me $600+ to replace.

 

[aerozoche]

Any more news on whether this finally resolved your issue for sure? Have you actually replaced the EGR valve yet or just been driving with it unplugged?

Just wondering because I think I have the same problem, but deciding whether to start with the Cat. or the EGR valve - both expensive, though EGR is easier to replace myself.
I need to get it do it's thing and then unplug the EGR to see if that fixes it immediately.
I've also wondered if a clogged Cat. would contribute to EGR malfunction/erroneous signal (so getting EGR symptoms when it's actually the Cat. increasing exhaust pressure and messing up the EGR)

I'll be watching for news on your case... hope yours is fixed!

 

[markag]

Any more news on whether this finally resolved your issue for sure? Have you actually replaced the EGR valve yet or just been driving with it unplugged?

Just wondering because I think I have the same problem, but deciding whether to start with the Cat. or the EGR valve - both expensive, though EGR is easier to replace myself.
I need to get it do it's thing and then unplug the EGR to see if that fixes it immediately.
I've also wondered if a clogged Cat. would contribute to EGR malfunction/erroneous signal (so getting EGR symptoms when it's actually the Cat. increasing exhaust pressure and messing up the EGR)

I'll be watching for news on your case... hope yours is fixed!

Well, it has been about a week so far, and my car has driven much much better then it has in a long time. I think the EGR was the root cause of my acceleration issues. I haven't replaced it yet, I've just been driving around with it unplugged.

For me, I am pretty sure that my catalytic converter was clogged in addition to the EGR issues. Even before I unplugged the EGR, I had replaced the cat and saw great improvements in performance. I also saw fuel economy levels that I hadn't seen from my car in a year or so. I can get 30mpg highway again out of the 3.1 V6, and I was averaging around 26mpg highway before the cat replacement.

If you have any questions if the EGR is causing the problem, it just takes a minute to reach under the hood and remove the connector. You will eventually get a check engine light, but you will be able to tell if your car is driving better.

As far as the relation between a bad cat and egr issues, I'm not sure what the actual relation is, if there even is a relation. However, I can guess that the two issues are related. I just don't really know for sure.

 

[aerozoche]

Thanks,
It was very warm today and it was acting particularly badly, so i stopped and disconnected EGR wire - bingo! The problem disappeared. Yes, the Engine light came on pretty promptly, but problem was gone. Tonight i took the EGR off and cleaned it a bit, moved the valve a bit - and put it back on. A quick test drive seems to show it was back (with wire attached again)...
I tested the resistance on the EGR valve - it seemed in spec. Puzzled if EGR is problem or if Cat is causing EGR to feed bad info to the computer.

Let us know if you replace the EGR valve and it continues to run well with the wire reattached. I'm trying to decide whether to try EGR valve or catalytic converter first. EGR is half the price and I know I can put it on.... Cat is twice as much + not sure how exhaust work will go for me with hand tools in the Apt parking lot... mechanic estimated $100 to put in if i gave him the parts.

Thanks!

 

[markag]

Thanks,
It was very warm today and it was acting particularly badly, so i stopped and disconnected EGR wire - bingo! The problem disappeared. Yes, the Engine light came on pretty promptly, but problem was gone. Tonight i took the EGR off and cleaned it a bit, moved the valve a bit - and put it back on. A quick test drive seems to show it was back (with wire attached again)...
I tested the resistance on the EGR valve - it seemed in spec. Puzzled if EGR is problem or if Cat is causing EGR to feed bad info to the computer.

Let us know if you replace the EGR valve and it continues to run well with the wire reattached. I'm trying to decide whether to try EGR valve or catalytic converter first. EGR is half the price and I know I can put it on.... Cat is twice as much + not sure how exhaust work will go for me with hand tools in the Apt parking lot... mechanic estimated $100 to put in if i gave him the parts.

Thanks!

Thanks for the follow up. I haven't changed the EGR valve yet, and to be honest, I don't know when I'm going to get around to it. The exhaust manifold in my wife's car has a crack, and that is next on my list of things to fix. I'm not really sure what the relation of the Cat to the EGR is, if one causes problems in the other or not.

What I did to see if my converter was truely clogged was to remove it and go fo a testdrive without the cat on the car. Other then being freaking loud, I was able to tell that my car had a noticable improvement. If you end up taking the car to a mechanic, they should be able to tell if the cat is clogged by measuring the pressure in front of and behind the converter. That would let them know if it is clogged. The method I used was more of a "poor man's" method for testing it out.

Changing the converter is easy in theory, but it can be difficult in application. The bolts on the exhaust will most likely be rusted severly, and a long breaker bar, or some sort of impact will probably be a requirement of the job. You will aslo probably need 2 feet or so of extensions to reach the nuts on the exhaust manifold side of the cat. They are up pretty high and you wouldn't be able to get a wrench in there to loosen them. In my opinion, if you converter really is clogged, $100 isn't too bad of a price to have a shop do it. It might be hard to change it yourself in the parking lot. If you have the tools to do it yourself though, once you get past the rust, your battle is pretty much over.

I don't have air tools myself, but I did pick up an electric impact wrench from harbor freight of all places. http://www.harborfreight.com/1-2-half-inch-electric-impact-wrench-45252.html. It wasn't that expensive when I bought it ($35 for me), but it has been a life saver. I picked up a set of standard length and deep impact sockets in metric sizes for it too. It has worked great for me, and saves a lot muscle strain. It worked wonders on my rusty exhaust bolts. The harbor freight one looks just like the one from Kobalt http://www.lowes.com/pd_28180-11241...oductId=3307992&N=0&catalogId=10051&langId=-1 but for a fraction of the price.

 

[lexisdad1201]

I am having the exact same issues. Once again, only happens after the car has warmed up and driven for a while. Went into a store and came out and it started the poor acceleration. Lift off and reapply and hits 3k rpm and goes like a bat outta hell. I have been so stumped. I have previoulsy replaced plugs, wires, fuel pump(not enough pressure). I will try this out tomorrow and see if it helps. Thanks so much!!!!!!

 

[cgraves5653]

Im having the exact same problem, Any luck fixing this? my 03 malibu misses @ low rpms, when it hits 3100 rpm it comes out of it.. I tried a new egr and it acted exactly the same so I went back to the old one and just run it unpluged. It really has me stumped!!

 

[AliMalibuSS702]

Sounds like I have this problem also I drive a 2006 Malibu ss I can't seem to find the egr valve ? Any pointers