SO I have a 2008 Tahoe that is having an engine problem. It started with a rough idle that has progressively gotten worse.

I have pulled the codes and the first one was a cylinder 7 misfire. I replace all of the plugs with OE and it went away for a little bit. I then got an o2 sensor code and replaced the o2 sensor. This cleared up that code. Then I got a crankshaft position sensor code and replace the sensor and it went away. Then the cylinder 7 misfire came back. I replaced the coil pack, wire, and plug but still misfiring.

I did some research and it seems that this is a common problem so I have tried all of the things they have suggested, wires, plug, coil pack, fuel injector, throttle body and mass air flow sensor. It seems that every part that I replace makes the idle worse. When I put the throttle body on and went through the re-learn process it would idle at 3000 rpm and not change, so I put the old throttle body back on and idle is at 500ish and still rough. I really don't know what to do from here and hoping one of you smart guys can help. I really don't want to have to take it in to the dealer. Thanks, sorry for the long post.

Im not a mechanic but did you unplug the mass air while its running to see if anything changes?

Cue the Chevy haters..

I haven't tried that, but I will tomorrow, thanks!

Changing parts based on codes is an excercise in futility Codes for anything can be caused by 20 other issues and without the ability to observe real time actions of systems and sensors, you can waste a lot of money and time. The code readers just don't give enough background info 08 and up anything get a lot more complicate than even 07 models Brakes are not even as simple as they use to be, many require an automated bleed after pad replacement to have a good pedal. It's getting crazy.


You could have a catalist, mass air flow, intake leak, ground, egr, 02 sensor, accelerator pedal, vacuum leak, security system, ignition switch, injector, icm, bcm, etc kinda problem.

You'll save a lot of headache getting it on a instant data type scanner and then you can start making educated guesses.

So I'm gonna show some ignorance here, but is the dealer the only one that can do that on these trucks or do most shops have that ability. I know chevy has some wacko code stuff that only certain readers will pick up.

On that note does anyone have a good reputable shop near Enterprise or Troy that they would recommend for this type of scan. I can do the work, I just don't have the scanner.

If it has a slight chirping sound like water pump bearing or a belt, get ready to spend some dollars. Cam shaft and lifter.

Look in to getting the afm turned off

Most shops now have scanners that will give you answers. I don't know anyone in that area but I'm sure someone on here will be able to help. Any shop today that doesn't better be a quick oil change.

We have just over $60k tied up in software, diagnostic programs and scanners between cars, commercial trucks and heavy equipment. Then you pay annually or monthly to continue use or to update.

Thanks for the reply, I haven't heard anything like that from the engine. I really hope that it isn't something internal.

Check the in line fuse on the mass air flow.

Thanks for the help hoggin. I'll do some checkin around here and see if there is someone that I can take it too.

In the infamous words of the classifieds: I wish you were closer!!

Thanks, I'll check it when I get off work tomorrow.

RangeTechnology $200 simply plug it in.

Auto enginuity program. I have it for ford and gm. If i was closer I'd help you out. You can get the hardware with gm software for $400-500. Had to have it for my powerstroke and my gmc. Also going to use it to test and retrieve codes and run live diagnostic on test drive when going to get an 09-12 tahoe/yukon. With all tge computer sensors on vehicles now days its a must have to keep something like thus in your tool arsenal. The nice thing about auto enginuity is let's say you have a gm,you by the hardware for gm. Then you get a ford,etc. You buy just the key code for that make and download it. Then you're set up for 2 makes of vehicles. Cost me $450 for my ford program hardware then another 200 for my gm software.

it amazes me to how many people do not understand diagnostic fees. Just before I left auto zone I sold a Bosh to a guy to run diagnostics on a Mac. 12000.00

You can buy a OBDII Bluetooth adapter and purchase Torque Pro app for about $5 on your phone. It lets you read codes, shows quite a bit of information, and even reset codes.

Since the code is tied to the #7 cylinder, I would check the compression.

So I did a compression check and they were all between 149 and 155. #7 was 151 and #5 right next to it was 150 so not a head gasket or cracked head or block that I can tell. I have talked to another user that has a similar truck that said it was probably an AFM lifter that is causing the problem. Does anyone know a way to test that without taking off the valve covers? Thanks

"rough idle" ??

Very noticeable or just not running like a sewing machine?

AFM (active fuel management) is notorious for giving problems. As someone already mentioned, it usually starts with lifters and possibly a camshaft.

Does it use any oil?