1989 Silverado 5.7 Auto, Code 43 Rough Idle

[lapi6436]

I recently bought a 1989 Chevrolet Silverado 1/2 ton 4X4 regular cab long box Brand New 350 and 700R4 Transmission. It only has about 1500 miles on the truck as of now. When I bought the truck it idled VERY high and never seem to come down even when the engine was totally warm in neutral or in gear, so I thought it was a vaccum leak. I checked everything on the throttle body with carb cleaner and found nothing, so I took out all of the fittings in the throttle body, thread taped all of them and re-installed them, didn't help. I tried the throttle position sensor and didn't help. I changed the EGR valve, IAC Motor, air filter Battery cause I needed one and fuel filter and it idles rough (but lower idle) when warmed up especially in gear (almost dies) and now I get a Code 43. The throttle injectors look like they are spraying good. The code 43 comes on when I am hard on the throttle. Mechanic shop in town said that sometimes the rebuilt engine require more initial timing to get the engine "ping test" to pass. Supposedly, If it doesn't pass the test it will retard the timing and set a code 43. So, this shop had to go as far as 10 degrees initial to get the engine to finally ping, so they said it was done and come get the truck (3rd time it's been there). By the way I'm running 91 octane fuel. The truck ran better than ever before for about 2 weeks. Now it idles Way too low, and sets the code 43 (electronic spark control) and pisses me off. When the truck was in the shop they also Made sure the TPS Voltage was where it needed to be at idle. ANY IDEAS PLEAS!!!!

[MT-2500]

The only timing is to set the base time.

If after seting base time check out knock sensor operation.
Code 43 is often caused by knock sensor wiring or bad connectors.

In the repair manual there is a replair flow chart for oode 43.

Let us know how it goes.

[herkyhawki]

http://www.enginebuildermag.com/arti...vy_19131l.aspx

Rebuilder’s survival tip: The main wiring harness runs along the right valve cover. It has a "dip" in it that is supposed to go under the heater hose. If the installer turns the harness upside down so the "dip" goes over the heater hose, the harness is close to the plug wires and it will induce a small current into the harness when the engine is run hard.

This small voltage in the circuit for the knock sensor is all it takes for the computer to "think" that there’s erratic spark or detonation present, even though there really isn’t a problem, so it sets a "Code 43" after a road test. The computer always checks the spark control circuit at start-up and sets a Code 43 if there’s a problem in the electronic spark control circuit, but it should never set a Code 43 after it’s been running down the road. If it does, then you’ve got the "Mysterious Code 43" that is probably caused by the high voltage plug wires inducing a current into the harness. We have fixed several of these pickups with this problem by rerouting the harness under the heater hose.

[lapi6436]

When I got home a week ago I checked the wiring harness you talked about to see if it was routed wrong and in fact IT WAS. So, I popped the heater hose off and installed the harness underneath. Re-installed everything, topped off the coolant that i lost in the process, took it for a drive and it didn't help. I AM NOT GETTING THE CODE 43 ANYMORE!! But it still has an "idle surge" that it most noticeable in drive with the brakes applied. I don't have a tach in the truck so I don't know specific RPM, but it is surging approximatly 200-300rpm. I am thinking it is one of two things. Either the fuel pump, or a vaccuum leak in the brake booster system somewhere. Like I said earlier, I already changed out the fuel filter, but I read on another post somewhere, where someone had the exact same symptoms, chenged out the fuel pump and it runs perfectly. What do you guys think???

[MT-2500]

Sounds like you need to check fuel pressure before throwing parts at it.

[t.b. motors]

well i dont know if this is going to fix your particular problem but i did 3 days worth of reading without finding the right answer and i had the same symptoms engine wouldnt over heat BUT the whole engine would get hot the hood the fenders everything so hot you couldnt even touch it it would pop out of the exhaust and had no power everytime i would put it in gear it would misfire even worse if not shut off so i took the matter into my own hands i want you to give something a try go to the auto store and buy an intake manifold gasket set and an egr valve gasket pull your intake off dont pull the tbi off as well just the intake right under the egr you will probably discover both ports are completly clogged up clean it up nice with some brakleen and a flathead screw driver once your done pull the egr clean that up nice to and flush the whole thing out with some brakleen. put the new gaskets on with the newly cleaned bores and youll probably discover that your problem has dissappeared. im never on hear i just wanted to come in to tell you to give what worked for me a try if you do have anymore questions send me an email at [email protected]

in the begining i also replaced tps, iac, distributor plus the cap and rotor wires plugs injectors fuel pump fuel filter new fuel lines all the way map sensor coil cts anything electrical that had a plug got replaced with a new egr from gm and none of that fixed it. i spent 2 hours total doing as i just described to you and im seeing power with this truck that i have never seen before. goodluck

[tblake]

Sounds like the next thing I would do is pinch off the brake booster vacuum line with a vice grips to see if the surging stops.

Then Make sure the timing is set correctly with a timing light.