Engine running rough?

RobtZ71 · April 20, 2004

I just replaced all the spark plugs, changed the PCV valve, and did a throttle body cleaning. Now, I didn't have any problems before I did all this stuff now, my engine, at idle, stutters and acts like it wants to die.

The spark plugs are AC Delco Platinums (like everyone suggests) and they were properly gapped at .060. I don't think the throttle body cleaning and PCV valve could cause this.

I think I may have messed something up. While I was wrenching out the plug in the very front on the drivers side, theres an electrical clip connecting to something that bolts into the engine block (I don't know what it is), I broke it trying to unscrew the plug. It was a plastic piece but, the wires still seemed to be intact.

Does anyone know what that part is or a P/N so that I can replace it. I don't have the patience to take my truck and have someone else look at it and tell me there's nothing wrong.

Any ideas????

Rob

Butch 02 Denali · April 20, 2004

You didn't say what year it was Rob, but it's probably the coolant temp sensor. Does it run better when it warms up?

Check the connector to the MAFS too, if it's loose it could run crappy like you describe too.

Butch 02 Sierra Denali

RobtZ71 · April 20, 2004

Sorry, it's an 00' 5.3 silverado.

It is really spiratic while cold or hot.

What's the MAFS and where is it located?

Thanks for the response.

Rob

JimG · April 20, 2004

MAF = Mass Airflow Sensor

It's located in-line with your airbox intake to the throttle body. Look at the big tube leading from the air filter housing up to the engine. Somewhere on there you'll see a 3-wire (I think it's 3 wires) connection. That's connected to the MAF sensor.

Stupid question: Are the spark plug wires all tight on the plugs??? Also, did you replace the wires? Or just the plugs. Almost sounds like the engine's missing and a bad or not fully seated wire could do that.

RobtZ71 · April 20, 2004

That is a very good question. I did not change the wires and come to think of it, there where a couple wires that were very difficult to remove and I may not have seated them well enough on the plugs or ruined a wire in the process. I'll check the wires again.

The only reason why I wouldn't think that the engine is missing is because it happens spiratically during idol. Unless it only misses every once in a while. I haven't had anything come up on the message center either, wouldn't a miss cause a check engine light to come on.

The only experience I've had in this area is on my 66' ford bronco with a 289 ci engine and when a plug isn't firing the engine would backfire. I don't really know anything about these new engines.

Would you recommend changing the wires as well, I thought these trucks weren't supposed to have a full tune up until 100k. I changed the plugs cause those things aren't that reliable.

Thanks for the MAF answer.

Rob

asilverblazer · April 20, 2004

For what its worth my 88 S-10 Blazer (big pile of ) needed a tune-up, back firing and missing badly, no check engine light came on on it. On a newer truck I wouldn't be surprised if a light should come on.

kdm101 · April 21, 2004

I'd consider replacing the wires first. It's quite possible, and most likely, that you damaged a conductor when pulling the plug boots off the old plugs. Those things tend to "glue" themselves on over time.

If that doesn't solve the problem, don't rule out that you have a bad plug yet. Even though they're new, sometimes, you get a bad one.

az'03Silverado · April 21, 2004

I'll second that. Definately sounds like the wires. Especially the ones with the long, straight plug end. The conductor on those is way up inside and it's really easy to not get it on all the way. And, they do damage very easily.

REDZ-71 · April 21, 2004

Have you performed PCM Idle Learn Procedure?

( Anytime the PCM or the battery is disconnected, the PCM loses power, or the PCM is reprogrammed, the PCM’s learned idle position is lost. The engine idle is unstable when the learned idle position is lost.)

Here is what you should do to return the learned idle to the correct position:

Automatic Transmission

1. Turn OFF the ignition.

2. Restore PCM battery feed.

3. Turn OFF the A/C controls.

4. Set the parking brake and block the drive wheels.

5. Start the engine.

6. Let the engine reach a normal operating temperature (176 F).

7. Shift the transmission selector into drive range.

8. Allow the engine to idle for 5 minutes.

9. Shift the transmission selector into the park range.

10. Allow the engine to idle for 5 minutes.

11. Turn OFF the engine for 30 seconds.

and now restart the engine - this should solve your problem.

I experienced a similar problem after taking off the throttle body to clean it. After performing the above procedure, rough-idle was gone. And now my 5.3L runs as smooth as new.

Manual Transmission

1. Turn OFF the ignition.

2. Restore the PCM battery feed.

3. Turn OFF the A/C controls.

4. Set the parking brake and block the drive wheels.

5. Transmission in neutral.

6. Start the engine

7. Let the engine reach a normal operating temperature (176 F).

8. Allow the engine to idle for 5 minutes.

9. Turn OFF the engine for 30 seconds.

Hope this helps

JamesB · April 21, 2004

While you are checking all of the plug wires etc also double check all of vacuum lines. A loose vacuum line can do weird things...

James.

bandera · April 21, 2004

Had a similar problem on my 2000 Z-71 with 5.3. It had about 52,000 miles on it and had a slight rough idle, so being the good "preventaive maint. fool", I put in new A-C plugs (just like the factory originals). That seemend to help a little. About three months later it started running a little rough and would "shudder" at 40-50 MPH. Checked EVERYTHING: cleaned throttle body (took it completely off), cleaned my K&N air filter, cleaned the MAF sensor, took it to the dealer and had the fuel injectors cleaned and updated the computer. Still ran the same! Took it back to the dealer the next weekend and they called me to say it was BAD SPARK PLUGS (three had cracked insulators) !!!! They wanted about $270 to change them out. I said no way! I could not believe it, but sure enough you could see hairline cracks. Of course I could not find my receipt to try to get a refund or replacement. So I put some new ones in (same type). Been perfect ever since. I don't know why the plug insulators cracked. Did not spash any water that I know of in there or wash the engine, so I don't know?????

citydriver · April 22, 2004

This may sound like a dumb question

But did you use the correct size SPARK PLUG SOCKET?

The reason I ask is cause the old sockets will fit the hex,but r too short for the plugs insulator(ceramic) causing them to crack....but I also agree that a bad plug wire or connection could also be the cause

bandera · April 22, 2004

Oh yeah, I made sure of that. I didn't want to have to go through all of that again. Plus I would wonder why it took three or four months before the problem surfaced. You would think that if I did crack the insulators while installing them, the problem would show up immediately. Just something you should consider while trying to figure it out. Let us know what you find.

RobtZ71 · April 22, 2004

I ended up checking to see if I had seated the wires on the plugs correctly and found that one plug wasn't on all the way. This seemed to solve the stuttering problem for the rest of the day but, it came back this morning. I will replace the wires, I hope that the plugs are still ok, I don't want to spend another 50 buck replacing those things.

I also want to try the PCM idle learn procedure. After I cleaned the throttle body, I replaced the plugs and started the engine without connecting the the air intake to the throttle body and the engine died, then I connected it and started the engine, and everything seemed to work fine. I wouldn't think this would cause the problem but, I guess you never know with these newer vehicles.

One question on the PCM idle learn procedure....should I disconnect the battery and then follow all the steps or just try it as is.

The spark plug socket was the correct size. I bought a new one with the plugs and used one of the plugs to make sure it was the right size.

Thank you, after I try some of these other suggestions, I'll be sure to let everyone know what the results are.

Rob

FDNY-Denali · September 28, 2004

Have you performed PCM Idle Learn Procedure?
( Anytime the PCM or the battery is disconnected, the PCM loses power, or the PCM is reprogrammed, the PCM’s learned idle position is lost. The engine idle is unstable when the learned idle position is lost.)

Here is what you should do to return the learned idle to the correct position:

Automatic Transmission

1. Turn OFF the ignition.

2. Restore PCM battery feed.

3. Turn OFF the A/C controls.

4. Set the parking brake and block the drive wheels.

5. Start the engine.

6. Let the engine reach a normal operating temperature (176 F).

7. Shift the transmission selector into drive range.

8. Allow the engine to idle for 5 minutes.

9. Shift the transmission selector into the park range.

10. Allow the engine to idle for 5 minutes.

11. Turn OFF the engine for 30 seconds.

and now restart the engine - this should solve your problem.

I experienced a similar problem after taking off the throttle body to clean it. After performing the above procedure, rough-idle was gone. And now my 5.3L runs as smooth as new.

<{POST_SNAPBACK}>

I just installed a K&N FIPK, and at the same time, I changed my Spark plug wires to Taylor ThunderVolts 10.4's. My engine lately has been running a little bit on the rough side when I am at idle or at a stop light. Also, I feel as if I lost some power now that I have installed the K&N.

Do you think that it is neccessary that I do this procedure?