89 Chevy Silverado issues.

I have an 89 chevy k1500 with the 5.7 engine. have had the heads reworked and all top end gaskets replaced. it had a blown head gasket. I bought the truck broke. I have had surging and idle problems ongoing. I have replaced the IAC, coolant temp sensor, t stat, battery, radiator, rebuilt TBI, checked EGR valve, checked for vacuum leaks, checked and cleaned fuel filter, ran injector cleaner thru injectors, checked all spark plugs, wires and didtributor and module all good. set timing to specks. After replacing failed stuck open thermostat, idle improved, backfire stopped, and I am actually able to drive the truck. accelerates very strong, but has slight hesitation on take off, and when warm, stalls sometimes at idle, then starts surging. like the engine is trying to find its fuel /air balance. check engine light comes on and off intermittantly and sets codes 43 and code 44. no weird noise coming from engine, no blue or black or white smoke, thermostat opening and closing as it should, coolant temp running around 180.F I only have a digital Volt Ohm meter, and am really not sure what else to check. I think the codes may be cause and effect,. I think the knock sensor may be caused by the engine jumping around or pinging due to what ever is causing the code 43. what I would like to know, is what is it that usually causes the codes 43 and 44 on these old trucks. The gas is fresh, the 02 sensor wire down from the cat is connected. somewhat of a mystery though, the exhaust manifold on the engine, which is a 92 model, has a hole for an 02 sensor. I just bought another sensor and screwed it in to block the hole. the wire on the dummy sensor isnt hooked up. So im wondering, why the 89 chevy k1500 had the O2 sensor down under past the cat, and the 92 engine has it right in the exhaust manifold, or is it that these manifolds are off of something totally different. and if it matters that the 02 sensor is downstream from the cat. anyway, im trying to determine if I really have a lean condition, or if the o2 SENSOR is not working . it seems to act up more when warm, or closed loop. thats why im thinking maybe the o2 sensor is bad. I could probably just swap the new dummy sensor with the old one and see what happens, but I want to know how to test it. Im tired of just guessing and buying parts. Also im thinking of getting a scanner that reads live data, Ive heard the Elm And torque pro are good for DYI mechanics such as myself. any input much appreciated. me and my son have worked on this truck since last summer, as a project, and its time to finish her up. its hard to teach someone to drive a standard when it stalls at idle or take off.

The elm and torque app are a good choice for diy, but since you have an obd1 vehicle, it will not help you out here. That is for 1996+ vehicles.

What did you do to test for vacuum leaks?

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I replaced intake manifold gasket after having the heads rebuilt, replaced TBI gasket, removed and tested EGR valve,replaced EGR valve gasket, removed, tested and cleanede PCV valve, checked all vacuum hoses, sprayed carb cleaner around intake gasket area with engine running. replaced questionable IAC motor and its gasket, . cleaned throttle plates in TBI.

did not mess with throttle butterfly gaskets

You mentioned it was pinging. Have you confirmed proper distributor timing or timing gear alignment?

did a new throttle pos. sensor come with the new throttle body? maybe try checking the tps signal with a multimeter and see if your getting a voltage thats bouncing around.

Yes I set base idle by unplugging the tan wire near the firewall, then verifyed after motor was running that it was advancing.

I didnt check anything on the TPS, didnt even remove it. I was wondering if it may be the problem though, when truck is surging and almost dies, if I GENTLY rest my foot on the gas pedal to just touch the throttle, things smooth out and idle is still a reasonable RPM according to sound, I dont have a tach.

the surging isnt real wide ranging , its easily noticed, but not from real high to real low.. its from normal idle to almost stalling then it repeats. almost like its trying to idle too low, and the engine notices the rpms too low, and speeds it back up.

I didnt replace the throttle body, I rebuilt it, but didnt touch the TPS.

The check engine code was 43 and 44. intermittent. I didnt actually hear it pinging, or see motor jumping around, or knocking or tapping.
The truck never threw the 43 and 44 code until we took her on her first road test. even before we replaced the faulty t stat and IAC , it was running horrible yet never threw a code. I unplugged the coolant temp sensor while it was running just to see if it would throw a code, and it did. I replaced the coolant temp sensor even though it ohmed good, just because of how critical it seems to be . Im usinf either Ac delco, dephi, or duralast wells parts if I can get them. replacing the stuck open t stat made a HUGE difference it how it runs.. it basically runs very good now, other than that very low surging idle and stumble and die on take off sometimes. shes breathing thru the cat and an old cherry bomb muffller and burning very clean. I havent seen even a puff of smoke come out of the pipe since we changed the t stat.

should I back probe the connector while its running and set meter to dc volts?

I dont knows if it matters but I put a bottle of lucas fuel injector cleaner in the tank with abt 3 gallons of gas. I noticed it is very thick. Im hoping that the cleaner didnt cause the pinging or 43 code. I ran most of that out, and added 10 gallons of 89 octane fresh gas. I may disconnect the battery and erase the codes, and take it for another ride around the neighborhood.

Replace tps is my bet. They usually live in that region of travel from idle to quarter throttle and probably not getting a steady voltage at idle. I believe my 93’ had a slight adjustment where as my 97’ doesn’t. So check what the voltage should be at throttle closed. If it were me I replaced everything when rebuilt tbi ‘s, but a great time learn and teach some voltage testing on an easy to get to component.

thanks I will try it. I have a 94 silverado as well, so I may be able to do a comparison of what the voltages at the tpi are. my 94 runs exceptionally well. When we bought the truck,(the 89) , the intake with TBI was sitting in the bed of the truck, exposed to the weather. they had a drunk working on it and he made a nice mess for me.
when I first start the truck cold, it lopes for abt 15 seconds, then levels out until closed loop then gets goofy again. Before replacing the thermostat and Iac, it was running on the rich side, and right after fixing that, it went lean. something is causing it to want to idle too low. it will idle down so low the oil pressure low indicator light flashes . ive heard the fuel pump and oil pressure sensor were linked on these trucks, and ive wondered if my problem has something to do with that. My oil pressure gauge is all over the place at idle and before engine surges down really low, like to zero the oil pressure gauge will spike to max, them to zero. it really seems like the computer is seeing something that isnt quite right, and tries to compensate. whatever it is, is intermittent as well.

its amazing how good these trucks run when everything is right, but quite frustrating trying to get everything exactly right, they are like babies, you got to give them what they want or they raise cain. ha

what scanner could I get that will read live data on this truck. im not going to invest in a 1,000 dollars scanner for DIY use. I would think there is something in between the paperclip and the snap on ? if I could see exactly when it went into closed loop, when it was pulling fuel away by trimming the rate, the tps position percentages, o2 data ect all real time, it would be wonderful.

That is a little odd with pressure gauge. And yes, the oil pressure sensor on the back of the block completes fuel pump circuit while running. I would check tps voltage first before buying any parts. Knowing the exact value isn’t important right now, you just want it to be steady at idle. At idle in this case because that’s where your having a problem. Usually you would sweep its full range with some kind of graphing multimeter or scope looking for spikes or weirdness. It should be something like 1.2v to 4.9v +\- closed to open. The closed voltage should be consistent as well meaning if you snap throttle it should return to the same voltage.
I still keep my old otc genisys scan tool for these old obd1 cars and works well even with newer cars and has bidirectional control as well. Mine is good to ‘05 but updates are available. You can probably score one on fleabay for about $500

my oil pressure sensor sits right above the oil filter housing. its inside a cone . I dont have the one next to the distributor,. I wonder if it is bad as well. likely the original oil pressure sensor.

it would seem that unless there is a reference voltage, there would be no voltage to the tps during idle, as the Iac, coolant temp sensor, and ECM are supposed to regulate idle exclusively. I understand though that it is possible to be shorting or bleeding voltage. throttle plates should be completely closed during idle is what ive read.

Ok. I did the tps voltage test. key on engine off 4.95 reference signal from pcm, good, .0.5 volt signal from tps to black ground wire good. check black ground wire, to engine ground . good. I plugged harness back into sensor back probed and started the truck. truck was surging pretty bad and voltage at sensor was .5 volts. I snapped the throttle and the voltage increased. once rpms settled down after snapping throttle, it started idleing alot better. I then went to the tps harness connnector and started wiggling it a bit to ensure it was plugged in good, and it started surging again. im thinking that the terminals in the tps might be squirrely or the sensor pintle is mechanically sticking. im going to replace the tps sensor and see what it does.. I saw from the wiring diagram that the sensor also gets an input from the coolant temp sensor. there was no fluctuation of the voltage at idle. it remained steady at 0.5 volts.