Surfurban

Hi everyone. Many thanks to our past, present and future veterans - Thank you for your service!

I have a 2001 Suburban 1500 2WD w/ 5.3L engine and about 140K on the odometer. I recently moved from southern Florida to South Carolina and the temperatures have been significantly cooler. I noticed on a morning where it was in the upper 30's that when I started the truck the idle was struggling to remain steady and would almost stall. After about a minute or two it was fine. It has only happened when the temperature outside is very cold. I haven't seen it happen during warmer weather and this is a recent thing considering I've only been here for 1 month (it was not happening in Florida). A fluke? Maybe. Here's what I've done: I took her to a local repair shop and they pulled no codes but did detect a slight misfire in cylinder #8 - but then, the engine was already warmed up. I took her home and replaced the coolant temperature sensor and spark plugs (gapped at .060). I also sprayed brake cleaner around the intake manifold areas where it bolts to the engine and noticed no change in idle. My next step is to drop it off at the repair shop and let it sit over night so they can do a cold start (on a cold morning) with it connected to the diagnostics.

I've posted a video here. Note that I had already started the truck moments before, shut it down and restarted. The computer is controlling all of the revs up and down; I did not touch the thottle at all during this video. At about 1:05 you'll see it surge. Any thoughts? Throttle position sensor? MAF sensor? Obviously don't want to be throwing money at it.

Video (turn your sound on obviously):


Thanks!

Surfurban

Here's an update that hopefully others can benefit from since I had no replies. I checked the torque on the intake manifold bolts and they were all within spec. I had an extra fuel pressure regulator from a previous 'burb years ago so I replaced it. Then, after re-inspecting vacuum lines I found a leak in the upper rubber boot of the line leading from the intake manifold to the fuel pressure regulator. Dry-rot seems to have reared it's ugly head there and as a quick-fix I wrapped it tight with electrical tape until I get a replacement. Cold idle issue appears to have gone away.

HAPPY THANKSGIVING ALL!

kevinkpk

Looking at the idle rpm drop, my guess was fuel pressure regulator

Surfurban

Since replacing the FPR over a month ago the cold idle issue consistently got worse with the colder weather. I re-torqued the intake manifold bolts but there was really no change. Codes P0300 for misfire and lean banks P0171 and P0174 kept popping up. I pretty much knew at this point it was definitely a vacuum leak somewhere at the manifold. A few days ago I again tested the intake manifold with water around the flanges and decided it was definitely the culprit after seeing a bit of white smoke out the exhaust and rougher idle. During cold idles immediately after starts I could hear the hissing too. Got some time the other day to replace the gaskets and now even with 20° morning temperatures she starts and idles fine. No visible cracks anywhere on the manifold either. $50 and a few hours is all it takes. Well, that and some damn cold/numb fingers, haha! Hope this helps anyone else with the idle issue(s).