Out of ideas - suggestions needed

[GMnutbag]

I have a 1997 Cheyenne cab & chassis, C3500, 5.7L vortec, 2WRD, 2DR, auto trans, engine code "R"
I bought the truck over 10 years ago with a blown engine. The odometer shows 156K. The seller assured me that the tranny was replace 12K ago when I bought it. I finally got time to work on it. I put in a remanufactured engine. I also replaced EVERYTHING with the engine. It starts up fine, runs about 2K rpm for about 8 seconds or so. But when the idle comes down it immediately starts to surge in RPM's till it dies. If I unplug the mass air flow sensor it seems to run perfectly. I can then plug the amf sensor back in and it continues to run fine. If you shut it down it just repeats the problem. I have the original maf sensor and 2 brand new ones and it does the same thing no matter which one is hooked up. Here's a list of all the new things besides the engine that I've replaced more than once trying to figure this out. It has brand new air intake temp sensor, mass air flow sensor, idle air control sensor, throttle position sensor, MAP sensor, EVAP solenoid, EVAP purge valve switch, upper intake manifold (plastic), fuel pump, fuel tank, fuel filter, air filter, crankshaft position sensor, camshaft position sensor, oil pressure switch/sensor, coolant temp sensor, radiator, main computer, all fuses are good and correct, distributor, coil, ignition control module, spark plugs & wires, EGR valve, fuel spider injector system (located in upper intake manifold), anti-knock sensor, intake manifold to head gaskets, fuel pressure regulator, and no vacuum leak of any kind. Even if I've missed something in this blog, I can assure you that it's been replaced at least twice. I'm just at a dead end for something to look at or check out that could cause this problem. If you've taken the time to read this story, I thank you and welcome any insight you may have. Thanking you in advance.

 

[0xDEADBEEF]

I had something very similar happen with my LS swap. It would not run with the MAF enabled, ran fine without it. Unfortunately, I don't think my fix will help you as I swapped the coil packs around and it suddenly worked.

It might be an issue with the wiring or grounds. I think that was my issue on the LS swap.

 

[docstoy]

So if you pull,push or manipulate wiring to make does it do same thing ? Have you looked at maf sensor connector and tried pushing and pulling wires to see if they move , could possibly be wire terminal in maf plug not latched into connector or terminal that has lost tension and not making good contact until you cycle connector , reasoning there is you have a lot of spare parts.

 

[docstoy]

Went and looked at my '97 c3500 R 4l80e, short harness from main to maf/at, is seal still on connector ? That could cause movement if not there, and terminal pins look to be push to seat , if you do decide to remove and retention wires & don't have terminal tools you may be able to use small paperclip, you'll have to straighten long side and where the space is at top center of terminal insert tool and push in while holding onto wire, you'll also need to get seal on back side out to give you clearance to remove terminal, but push on paperclip and should be able to when terminal latch releases then pull wire out while holding paperclip or tool in same position, it won't take munch movement of paperclip or tool to release latch if having problem getting terminal out, do one at a time when you have it out take a small pick, screwdriver or paperclip at reform terminal so that it will have tension on maf sensor terminals. Another thing one of the wires could be broken thinking of that by how harness hangs down because weight of harness will still have to remove terminal for repair . Be patient this can be frustrating. Good luck