2003 Tahoe 5.3 - Random Multiple Cylinder Misfire

[mcorbitt52]

For the past 6 months my 2003 Tahoe 5.3 V8 periodically gets a “random multiple cylinder misfire detected” (P0300 on low-end code reader).

There is no consistency. It goes weeks without surfacing, then can happen on an initial start-up, or after the Tahoe has warmed up and then turned off and restarted. It has never surfaced once the car has started and is running normal.

Usually the rough running clears up after 5-10 minutes. This week it surfaced after the Tahoe had not be run for a few days, and it had been a few weeks before it had run rough. The symptom lasted for a few days on short drives but this morning started and ran fine.

The Tahoe has 163K miles. I have owned it for 3 years but do not know what the past history of service. Recently I changed the sparks plugs (they looked like they were due), and then was planning to change the ignition coils and possibly the pre-converter O2 sensors. I also realize this could be a fuel problem.

If any of you have experienced this same issue and were able to resolve the problem, is there a logical step-by-step I should follow to narrow in on the exact cause of the issue? Given the mileage, is it also about time I change out these parts anyway?

Thanks for any assistance.

 

[Scottydoggs]

could be busted up cats clogging and unclogging. if you bang on them and hear them rattle inside you know they are bad.

 

[Fless]

Have the spark plug wires been changed?

 

[SnowDrifter]

What are your fuel trims and fuel pressure?

Are you using a dry filter or oiled filter? How's the MAF?

What did you gap the plugs to?

 

[Ilikemtb999]

I had this exact same thing on my 01 5.3 that I hunted down for months, turned out it was just a semi clogged injector. Changed it out and was back to normal. Could also be intake manifold gaskets as they’re known to go back if they’re not the updated ones.

 

[Doubeleive]

my exwifes 04 did that, basically ended up shotgunning it plugs, wires, coils and then to top it off a new MAF then it finally went away. It was all of those things combined as I discovered along the way, had a couple bad wires, couple bad coil packs, and a bad MAF. now she purs like a kitten again.

 

[mcorbitt52]

Have the spark plug wires been changed?

Spark plug wires are on the list to be changed this weekend. thanks for the feedback

 

[mcorbitt52]

could be busted up cats clogging and unclogging. if you bang on them and hear them rattle inside you know they are bad.

I had not thought about this. I will check it out. thanks.

 

[Larryjb]

Invest in a scantool. You can get some decent ones for less than $500. This could pay off with just one service visit, as long as you know how to use it properly. If your fuel trims are too high, that means that the computer is trying to add fuel to compensate for extra air that got in without being metered. A dirty MAF could cause this, but also leaking intake manifold gaskets. There are other possible causes for this. Here is a good video showing how a scantool was used to confirm a vacuum leak, and what was leaking:

(common causes of random misfires is also a leaking intake manifold)

Right now you're shooting in the dark with troubleshooting.

 

[tdemontigny91406]

Before you get crazy with everything how many miles? Last time spark plugs were changed? If they were hopefully not Bosch they tend to do that quickly. I'd pull the boot off the fpr (fuel pressure regulator) located on the fuel rail drivers side and see if there's fuel on the outside of the regulator if there is it's a bad regulator causing fueling issues causing it to bounce from cylinder to cylinder just my .02

 

[mcorbitt52]

I want to thank everyone for the feedback. Here's what I did following the feedback. Checked cat (no rattles), changed plugs ((gap = .060) and plug wires. The random rough running returned a few days later. I then changed the upper O2 sensors. It ran smooth with not issues for two weeks then the symptom returned. The rough idling still happens randomly but only at start up and once the engine is warmed and restarted it goes away. My code scanner indicates a P0120 - throttle/pedal position sensor/switch A circuit. I watched a couple of U-Tube videos, picked up a new sensor at NAPA today and started the replacement. Immediately I realized my throttle body is different than what the U-Tube videos show. Either the PO changed the throttle body or my 2003 5.3 had a 2004 throttle body put on at the factory. Regardless, the sensor is riveted on the right side of the throttle body and not the little sensor shown on U-Tube for the 2003. Some of my research told me that in years past when the sensor went bad on the 2004 version, it was necessary to buy the entire throttle body and sensor, until GM came out with a sensor repair kit. The sensor repair kit appears to clip on the throttle body. The throttle body plate that my sensor is riveted to is different than the plate that allows a sensor repair kit to be clipped to. Because my sensor is riveted, am I going to need to by the entire assembly, or are there other options? Thanks for any wisdom you can share.

 

[Erickk120]

Honestly I would buy a used one and call it good, they're are 50 bucks where I live. beats 200+ new and these things hardly fail, and if that isnt the issue you can return it and get it back so its a win win either way.

 

[MrBiggs228]

Had this issue as well. Chased it down for a few weeks. Changed plugs, wires and coils and it still lingered. End up being the cats were clogged

 

[mcorbitt52]

Thanks for all the helful replies. My 5.3 Tahoe has 162k. Here’s what I’ve done since original symptoms started
Cleaned MAF
New spark plugs and wires
New upper O2 sensors
New throttle body with throttle position sensor

Symptoms changed after replacing the O2 sensor. My Foxwell NT301 (low end) code reader indicated a problem with the P0120 Throttle Pedal Position Sensor/Switch Circuit A. So I changed out the throttle body/position sensor.

It ran better than ever on a test drive that afternoon.

Current symptom: On cool days (below mid 50s) engine runs rough until reaching operating temperature and restarting. Once it reaches operating temperature, if I turn the engine off and restart it runs fine. This symptom has been consistent over the past two weeks.

Any thoughts on this? Does the 5.3 have a cold start sensor? If so, could this be a likely problem?

 

[Kraig]

On the current cold start issue, without any more info, I vote for intake manifold gaskets.

 

[mcorbitt52]

On the current. Old start issue, without any more info, I vote for intake manifold gaskets.

Kraig, I appreciate the response. I'm only a backyard mechanic, so I'm curious how the intake manifold affects the current symptom which is: when starting the Tahoe it runs rough until it's warmed up and then restarted. I'm not sure how long it would run rough if I didn't restart it, as I always turn it off once up to operating temperature and then restart so it runs smoothly. Would appreciate your feedback as I really enjoy learning more about engine operation.

 

[Tonyrodz]

Sounds like it might be your iac sensor. Rough running/stalling when cold, but once it's warmed up, starts normally, idles good and runs smooth. Right?

 

[Kraig]

Kraig, I appreciate the response. I'm only a backyard mechanic, so I'm curious how the intake manifold affects the current symptom which is: when starting the Tahoe it runs rough until it's warmed up and then restarted. I'm not sure how long it would run rough if I didn't restart it, as I always turn it off once up to operating temperature and then restart so it runs smoothly. Would appreciate your feedback as I really enjoy learning more about engine operation.

A cracked, leaking gasket would cause it to run lean when cold and may seal up as things get warm. I’m curious if it would clear up if you didn’t turn it off and turn it back on.