jrlinden

2003 Chevy Tahoe LT v8 5.3L 4WD - Reduced Power
Vehicle would buck under load and run rough but only showed codes related to the Mass Air Flow Sensor - Sensor is recently replaced but cleaned with Mass Air Flow Spray. No change in symptoms.
Symptoms aligned more with a faulty Throttle Position Sensor (TPS) yet no codes indicated as I see in previous posts. No Reduced Power message shown on dash or indicated on codes. Replaced the TPS - ran great for several days but always has an issue trying to get rid of the Mass Air Flow error codes PO101, PO103, and a few other related to running too lean, but started, idled and accelerated just fine.
REMOTED STARTED the car for warm up - (factory installed option - not an add-on) when I entered the vehicle the reduced engine power was displayed and all the symptoms described in other posts, BUT STILL NO CODES related to the TPS were displayed other than those related to the MAF.
Stared to look for grounds shown in videos/diagram - Found only the one major firewall to engine strap - cleaned up (wasn't dirty or corroded) but is shiny now. No change.
Used the key to start (and stayed parked) several times, and randomly the car would either display Reduced Power with rough idle, low rpm's when accelerator depressed or it would start and rev perfectly the next time. TWICE when the key was turned to start the vehicle acted like no spark/no fuel - Battery is days old - and because of the dings that happen while starting it's difficult to hear if the fuel pump was clicking. Repeated attempts to start acted the same - cleared the codes - only the MAF sensor showed - and vehicle started perfectly and upon repeated restarts acted as described above - sometime perfect - sometimes REDUCED POWER.
Any Ideas? I plan to locate the ground wire out of the connector for the TPS and check the ground with a meter or try to trace the ground which seems almost impossible, but is there anything else I could do to narrow this down?

Silverfox103

Can't help you out with your specific problem, but I did have a very similar problem with a 1994 Caprice LT1. I had reduced power and the transmission didn't act right. Turned out it was the computer (PCM). Replaced that and it was good as new. Diagnosed at a transmission shop.

Tom

Buck1968

My 03 Tahoe would go into limp mode for seemingly no reason and was giving me code P1518, TAC module. Ultimately, this problem was caused by a wiring problem with the grounds. The repair was completed by my local Chevrolet dealership's service department, so I can't tell you how to make the repair, but this is what was written on my service receipt: "G104 improperly located on back of engine block. Relocated G104 to back of cylinder head and cleaned grounds. Traced wiring and found loose connection causing poor connectivity, putting strain, and causing heat build up. Corrected wiring issue and test drove. Concern resolved." I have not experienced any more problems with this vehicle since having the repair completed in March 2020. The source of this problem was very difficult for the technicians to locate. The vehicle was showing the P1518 error code, so before they found the burned out ground, the service department replaced a rear wheel speed sensor ($260.00) and the TAC module ($640.00), which may or may not have been causing the problem. If you are someone with the knowledge and equipment to check for a wiring short, I recommend you do this first. The sensor and TAC module may or may not have needed replacing (my guess is that the ground was causing the problem from the beginning).
I would start by checking all of the grounds--I think there are three or four of them-- and go from there.

repairman54

New MAF aftermarket ? Non GM sensors are not to be trusted, many reports of bad ones right out of the box. Use Genuine GM sensors only. Bad aftermarket stuff new out of the box complicates issues.
If codes say bad MAF, it most likely is.