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Discussion Starter #1
I've got a 2008 Malibu with about 5000 miles. In May or June I noticed a problem with engine speed control.



Consider driving along a flat highway at a constant 55/60 MPH with cruise set. The engine speed, on occasion, will jump up a few hundred RPM as seen on the Tach, stay there for a few seconds, then return to where it was. This happens with or w/o the AC on. Because the car is so quiet, it's hard to hear the engine speed change.



This problem actually happens with or without cruise control AND it happens at all vehicle speeds. The faster I'm driving the more the engine speed jumps.



I don't really feel the car surge or "droop" or anything.. my "seat of the pants" feel seems to be the same. On occasion it seems like I feel something.


It's been in the shop now about 4 or 5 times for them to fix. They've tested the cluster and found it working correctly. They've confirmed that the ECM is sending the same data as displayed on the tach. They've replaced an ECM and a crank speed sensor.



They say they've been on the phone with GM and GM says that it's a corrupted engine speed signal. So yesterday I was telling them how to troubleshoot that... I told them I think they should use the transmission input speed sensor (TISS) to confirm that the crank speed sensor signal is valid. If they match, then the problem is not a corrupted speed signal.


I asked the question about the possibility of the transmission slipping. He said that it should set a code if that were the case.



I've got experience in engine control from a previous job and have debated taking a day off work and telling them to let me use their Tech2 service tool while someone else drives. Based on my previous work experience I could write up other test procedures to debug the issue, but I shouldn't have to! I'd like to think that GM knows how to diagnose their products, but now I'm not so sure.



Anyone else have any thoughts or ideas? I have 2 suspicions... Some sensor that is an input into engine speed control (i.e. mass air flow) has an intermittent signal that their software is not flagging as faulty OR the transmission is slipping.



Thanks!
 

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Please keep us informed if and when you figure out the problem.
 

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Discussion Starter #4
Well, I got a call from the dealer and they said they had it fixed...

So I got there and he explained how GM feels that the problem is with a corrupted engine speed signal. They've already replaced the speed sensor and that didn't fix it, so they were looking at the wiring. He said they found one spot that was chafed and they repaired it and felt cofident it would fix my problem.

So I hop in and the first thing I do is get on the highway right next to the dealership. I drove about 5 miles and continued to see the problem. I turned around and called the dealership and told him I was bringing it back.

When I got there I explained to him again how they should look at other speed signals to see if they can confirm that the engine speed signal is valid or not. He then started talking about potential for the tranny to be an issue. I also explained that if it's not the tranny, then maybe it's another sensor that is an input to the engine speed control. Maybe one of those is intermittent and causing the engine speed control to goof up.

The thing that really pisses me off is that he said their techs drove it and didn't see the problem, but yet they managed to burn about a quarter of a tank of gas!!!! My tank was nearly full when I dropped it off and was down to almost a quarter tank when I drove it this afternoon. What the hell they doin'? Joy riding? Plus the fuel economy went from 26+ MPG to just at 24MPG. WTF are they doing???

I'm really starting to get fed up with this mess... I've debated asking to drive on of their malibu's to see if it happens on one of those.

Does anyone else see this problem on their malibu's? GM has already asked the dealer once if they're sure they're not chasing a non-issue. I've got video of it on my cell phone, too.

If they can't get it figured out tomorrow, I'm taking it to a different dealership... hell the one I bought it from is just a block from my job. The only reason I went to this one is because it's in my town and I know they can give me a loaner.
 

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hmmmm..........


maybe they had more than one tech drive the vehicle.
maybe they drove it more than once just to see how it did.
maybe they drove it at different speeds.
sounds like they're trying to help.
some problems aren't always easy to find and sometimes it doesn't always happen at the dealership.
sometimes it take multiple visits to correct a problem.

remember this...
that advisor doesn't make money unless they fix the car
the technician doesn't make any money unless they fix the car
the technician makes less money on a car under warranty for the same repair not under warranty and if he finds nothing wrong, he doesn't make anything, not even diag time, so he's going to try and find something. so why would he waste his time playing around in your car not making money.
if they can't justify a repair, they can't fix something for the fun of it, GM wont pay the claim.

they're in business to make money, they make money by fixing cars, whether it be customer pay or warranty, fixing the car makes them money.

it can aggravating at times, but its like a sick child, sometimes you take them to the doctor and miraculously they're fine.

if they blew off every customer like your thinking they're doing, they wouldn't be in business.
 

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Discussion Starter #6
....if they blew off every customer like your thinking they're doing, they wouldn't be in business.
I have no problem with them having to look at the problem multiple times, but when they say it's fixed (twice) and I can reproduce the problem in less than 5 minutes, then it's more than aggrevating. It's not a hard problem to reproduce.. it happens every time. There are no special conditions, there's no silver bullet that makes it happen. I find it hard to believe that they could burn a quarter tank of gas and not see it one single time. The only thing I can figure is that they drove it around town at 30 MPH for 2 hours rather than getting on the highway and getting up to speed and setting the cruise.
 

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It sounds like they are trying but i understand your frustration..i had the same problem with the dodge dealership they kept telling me it was fixed and it wasnt..so i got on the phone with Dodge and explained my situation and they sent a rep or someone i forgot the official name but when he got there they seemed to be on the ball and got the problem fixed, he rode with me and i showed him the problem and told him that i didnt want them to waste anymore of my time...so if it keeps happening that would be my next step epically if since it is a new car.. good luck
 

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lemon law?

im having kind of the same problem, but it has to do with the ECS, the car is currently at the dealer, and they have had it for a total of 7days, and ive only owned and driven for 5days. so with less than 400miles and already having problems im getting upset. but they are going to compensate for the issues, and if the problem isnt corrected i will be getting a new car.
 

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Discussion Starter #9
lemon law?

im having kind of the same problem, but it has to do with the ECS, the car is currently at the dealer, and they have had it for a total of 7days, and ive only owned and driven for 5days. so with less than 400miles and already having problems im getting upset. but they are going to compensate for the issues, and if the problem isnt corrected i will be getting a new car.
Here is info about the lemon law in Illinois:
http://www.ag.state.il.us/consumers/lemonlaw.html

I see you're from Texas. Here's info for you:
http://www.dot.state.tx.us/services/motor_vehicle/texas_lemon_law/default.htm
 

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Discussion Starter #10
Well, I've got my car back...

After having it since Tuesday, and going round-and-round with GM, they finally got a GM Support person that said that the behavior is normal. So to confirm this they drove another 08 BU that was on their lot with the same engine/tranny and saw it happening on that car. When I got there to pick up my car they had me drive the same car. Initially I was about to get a bit upset because in the first 7 miles it didn't do it one single time (by this time my car is usually doing it all the time). But when I turned around to go back I saw it happen. In a 14 mile round trip I saw it happen twice. Both times were on the return trip and one was just as we crested a slight hill. However, my car does it all the time, but I guess I can feel a bit better that GM says this is normal.

The guy from the shop that drove their car said that on the first leg of his trip their car was doing it a lot, but not on the return trip. Who knows...

So, to all of you out there that have the 4 cylinder/4 speed tranny, don't be surprised if you start noticing this as well.

BTW I checked my frame and am seeing the beginnings of the scuff marks that I saw mentioned in another thread somewhere.
 

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BTW I checked my frame and am seeing the beginnings of the scuff marks that I saw mentioned in another thread somewhere.
what are these scuff marks you speak of. I'll check my car out.
Thanks!
 

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Discussion Starter #14
I don't remember where I saw it mentioned.. but there's an issue with some seals being really stiff and they're textured, so every time you open/close the door it scuffs the paint around the door frame. Not noticeable at first, but does get worse the longer you own the car.
 
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