5.3L surges, rolls and stalls at idle
A few weeks ago I purchased a 1999 Silverado K1500 with 5.3L and 202,000 miles. K&N, headers with duals and about every factory option. The last owner for 80,000 miles did nothing but oil changes and let everything go when it broke so I am busy fixing many things. Wiper pulse board, mirror switch, defroster mode switch, rear calipers were froze forever (he thought the truck stopped fine!), ABS didn’t work, rusted speed sensors, tailgate hinges rusted off etc, etc. You get the picture. Lots of TLC needed but it runs and shifts good and the price was affordable so I took a chance. When I got it I noticed it surged and tried to stall when cold but it seems to run great once warmed up. I changed plugs, wires and fuel filter, pcv valve and it had a code P0449 so I replaced the EVAP canister vent solenoid on the intake hoping that would clear the CEL for inspection. I need to get the codes read again but last week it was O2 lean on both banks (probably just from the surging?). It has been in the teens and twenties here in rural, New York and every morning the truck starts instantly but revs over 2000 rpms for 30 seconds then drops to a few hundred and tries to stall then continues to surge and roll between the two. I have to hold the accelerator to keep it running. Once on the road it runs okay at speed but surges terrible at stop signs and I must throw it into neutral to keep it running. 15 minutes to the post office and parked for 2 minutes and no change. Another 15 minutes to town for a 5 minute errand and when I next start it, it runs almost perfect the rest of the way to work. If I park it until noon it still runs perfect. At 5 o’clock it starts and runs perfect. The next morning it is almost undrivable again for at least 20 minutes or, coincidentally, several start, stop and rest cycles. The prime complaint here on the Forum was the IAC control so I just changed that using the Helms procedure, which is key on 10 seconds, off ten seconds, start and idle 5 minutes, off thirty seconds then restart. It didn’t make a bit off difference. On my LT1 there was a similar procedure that reset the IAC perfectly and made a big difference in idle quality. Is there a different procedure to reset this IAC that Helms left out? My next thought is to remove and check the EGR, which, I remember, was also critical on my LT1. I just hate to throw another very expensive part at this if there may be another cause. The last owner claimed to have replaced two fuel pumps in the last few years and both O2 sensors just last year so he may have suffered with this undiagnosed surge problem for a while and never let on. The truck is fun to drive once the surge clears up and has never given me a problem except in the early morning until late last night. I came down a long hill to a stop sign and had to wait for several cars. Just as I was to pull out there was a “clunk” or “ shudder” ( I think I both heard and felt it but it was quick so….) Kind of like the tranny all of a sudden dropping into gear or??. Any way, it tried to stall and wouldn’t get out into traffic without backfiring and sounding like it was had a stuck carburetor float (if it still had one). Drove like crap the 20 miles home and barely got away from the stop signs. I haven’t started it yet today but don’t expect much. I almost think the whole computer memory should be erased so we can start fresh? Sorry this is so long but I was hoping to try a few more things before taking it to a mechanic and letting him throw parts at it. There goes my good deal. Thanks for any suggestions.