2003 Tahoe 5.3 - Random Multiple Cylinder Misfire

[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.