**FIXED!!**DEFINITELY***Super HIGH idle after multiple parts replacement - TBI 1990 K1500 350engine

[ZombieK5]

I just finished a major parts replacement on my 1990 5.7 Silverado.

TBI rebuilt with new injectors and sensors, new regulator, new throttle position and new IAC.

New PCV valve and new hoses all around. New alternator, new power steering, new spark plugs/plug wires, new distributor cap and rotor. New fuel lines, new gas tank and new sending unit. New O2 Sensor and new exhaust front to back. New EGR valve and a bunch of other stuff I'm forgetting. After a couple attempts to start, it finally fired up after fuel reached the tbi. Super rough to start out with then I realized I forgot to plug in the IAC. I plugged that in and it started right up but the idle is super high. I tried tapping the gas pedal to nudge the throttle but it didn't kick down. Also installed a new kickdown cable on the 700R4 transmission. I don't believe that would have anything to do with the initial Idle.

I did the IAC reset/calibration sequence.

Later, I Got a Service Engine Soon light.

I did the paperclip trick - Jump A & B OBD1

I got a single flash then two flashes then 20 seconds later I get FOUR short flashes. That repeated over and over.

Found 6 OBD1 Code sources and not one says what 4 short flashes are.

Now, the rpm's are DOWN but not where it should be. The new issue is the Engine is still surging up and down....it is doing this more than anything.

There is hesitantation when I quickly press throttle.

Any thoughts or recommended starting points? I attached a photograph of the sensor that has the open vacuum port.

Thanks for any input

 

[Bent77]

Yeah, do one thing at a time


Retime the distributor using the sequence s as you call it. You only move the dizzy with the connector wire unplugged. Set to 0, turn truck off , reconnect

Once that’s done restart. Worth noting that Tbi can take up to 6 cycles to relearn


After the dizzy is done, let’s see how it acts. Pcv valve could be the wrong spec or sucking air

do one thing at a time

 

[ZombieK5]

Yeah, do one thing at a time


Retime the distributor using the sequence s as you call it. You only move the dizzy with the connector wire unplugged. Set to 0, turn truck off , reconnect

do one thing at a time

The Dizzy wasn't moved When I replaced the cap and the rotor. The engine was timed before I did all the work. I can bust out my timing light and check the timing. I haven't checked the timing on a 350 engine and probably 15 years.

The thing that puzzles me is the engine ran fine before I did The work.

 

[gweber71]

Did you replace the gasket under the TBI when you did the other work? My truck all of a sudden had a high idle and it was due to the gasket failing. Another time I had the IAC fail and it caused a high idle. Sometimes new parts are bad right of the box. My truck does not like aftermarket IAC sensors, so I went back to a GM part from Rock Auto.

 

[ZombieK5]

Did you replace the gasket under the TBI when you did the other work? My truck all of a sudden had a high idle and it was due to the gasket failing. Another time I had the IAC fail and it caused a high idle. Sometimes new parts are bad right of the box. My truck does not like aftermarket IAC sensors, so I went back to a GM part from Rock Auto.

I replaced every gasket on the TBI including the base gasket. Also the new IAC valve is a GM original version. I agree that it could be bad out of the box but at the moment I'm giving it the benefit of the doubt. I have the old one however the spring did not fully function on it.

The surging is my biggest concern at the moment. I'm also wondering if anybody has a recommendation for a tachometer that I can hook up while performing this repair.

 

[gmbellew]

Code 24 is VSS. It could have been a stored code that will eventually go away. But if not, VSS could affect idle, as the ECM uses VSS to determine when the engine is actually at "idle." And when it is "off idle" the IAC doesn't close like it should to pull down the RPM to target idle speed.

 

[Wes Harden]

Is probably a code 44 which would fuel air. Exhuast lean code. Ecm is seeing under .3v ftom o2 sensor.

surging is typically a vacuum leak, or an injector not metering ascexpected by computer.

 

[ZombieK5]

Is probably a code 44 which would fuel air. Exhuast lean code. Ecm is seeing under .3v ftom o2 sensor.

surging is typically a vacuum leak, or an injector not metering ascexpected by computer.

Thx

Btw, two new GM injectors and new Bosch O2.

Just to be clear, the check engine soon light was flashing four times then nothing then four times then nothing. It's quite confusing but I guess that could be 44. I'll check the O2 sensor connection make sure it's okay. I'll clear the code and see if it comes back.

I'll go back through and check all the vacuum lines to make sure there is not a pinhole or a crack.

 

[ZombieK5]

Code 24 is VSS. It could have been a stored code that will eventually go away. But if not, VSS could affect idle, as the ECM uses VSS to determine when the engine is actually at "idle." And when it is "off idle" the IAC doesn't close like it should to pull down the RPM to target idle speed.

I'm pretty sure the VSS is on the 241 transfer case. I'm fairly certain those are connected properly but I will pull the connectors and put them back in again. The vehicle wasn't surging before I did the work so I would assume the VSS would not fail during the time it was unplugged. I unplugged the transfer case pigtails when I replaced the seals.

 

[gmbellew]

sorry, misread it earlier. code 44 is the repeating "4" for code 44 it flashes 4x, pause, 4x, repeat 2 more times. for a code 24 it would flash 2x, pause, 4x, repeat 2 more times. it flashes multiple codes from lowest number to highest number.

but a code 44 won't be set at idle I don't think. i think the lean and rich code parameters only set a code when off idle.

 

[Bent77]

The Dizzy wasn't moved When I replaced the cap and the rotor. The engine was timed before I did all the work. I can bust out my timing light and check the timing. I haven't checked the timing on a 350 engine and probably 15 years.

The thing that puzzles me is the engine ran fine before I did The work.

Understand, but also doesn’t mean those components are clocked 100% perfect. Trust but confirm

Heed the directions on setting the timing, it can make the tbi angry

 

[Wes Harden]

Or that the chain hasn't stretched, and instead of zero you are retarded. Comp should compensate, but surging is not going to be cause timing is off a degree or two.

What lead to all this maintenance was there a specific problem needed fixing ?

 

[Blue85]

It may be as simple as a vacuum leak. That's easy to test with a stethoscope or even propane torch. The TBI base gasket could have gotten out of place during assembly or the bolts were over-tightened. Anything with PVC or EGR could have been assembled wrong or a hose cracked during the process.

Do you have a scan tool so you can read the actual O2 signal?

 

[ZombieK5]

It may be as simple as a vacuum leak. That's easy to test with a stethoscope or even propane torch. The TBI base gasket could have gotten out of place during assembly or the bolts were over-tightened. Anything with PVC or EGR could have been assembled wrong or a hose cracked during the process.

Do you have a scan tool so you can read the actual O2 signal?

Checked EGR and the hose that goes to the back of the TBI with a vacuum pump and both hold vacuum.

I haven't checked the base gasket or EGR gasket yet.

I did the base idle calibration procedure again. It started and hovered around 1,000 RPM for a couple of minutes then drop to about 800 RPM and started surging. I turned the engine off and waited 30 seconds then turn the key on for 10 seconds and start at the engine.

It eventually settled down to about 750 rpm, where I think it should be (is 750rpm wrong?), then it started surging. It surges between 600 and 800 rpm.

While the engine was warming up it dropped down as low as 400 RPM but did not drop below 400 RPM once the engine was warm. I'm running it without the air cleaner on. The PCV valve and PCV hose are brand new. It is the correct PCV valve and it is OEM. The hose that runs from the driver side valve cover to the TBI collar is brand new with a brand new brass connector going into the valve cover. I was able to get my Craftsman tachometer, dwell meter and voltmeter from 1982 connected to the engine. The engine doesn't start like a modern fuel injected car and it takes about 5 to 10 seconds cranking before it starts. That is true even after it is warmed up. Once warmed up and I floor the accelerator there is a definite pause that sounds like a massive suction occurring from the TBI. it almost sounds as if it's not receiving enough gas for a brief few moments before finally catching up. I'm not sure if I mention the entire fuel system is new. New fuel lines, new fuel filter, new sending unit new pump and a new gas tank. There are no leaks.

I just ordered an OBD1 to Laptop computer adapter. Once it's here I should be able to get the O2 sensor readings as well as the throttle position sensor voltage. I noticed that my version of throttle position sensor does not have the ability to rotate it for adjustment. What I'm trying to say it does not have a oblong or oval shape screw hole that would allow tiny adjustments for calibration.

I am headed to work. I am off Sunday and Monday and will try and Conquer this problem some more.

Please continue inundating me with suggestions.

 

[ZombieK5]

sorry, misread it earlier. code 44 is the repeating "4" for code 44 it flashes 4x, pause, 4x, repeat 2 more times. for a code 24 it would flash 2x, pause, 4x, repeat 2 more times. it flashes multiple codes from lowest number to highest number.

but a code 44 won't be set at idle I don't think. i think the lean and rich code parameters only set a code when off idle.

I started the truck about an hour ago and the code was gone. I didn't reset the codes or anything. I am not a big fan of OBD2 however OBD2 definitely has advantages over obd1.

 

[ZombieK5]

Or that the chain hasn't stretched, and instead of zero you are retarded. Comp should compensate, but surging is not going to be cause timing is off a degree or two.

What lead to all this maintenance was there a specific problem needed fixing ?

The previous owner screwed a lot of things up. The exhaust was wrong and that started me down the rabbit hole. There was a series of oil leaks and transmission fluid leaks. I set out to fix those and as I took parts off I put new parts on. The power steering was leaking at the gearbox and the pump so I replace the power steering pump and the lines. It's holding fluid now. The oil cooler lines were leaking so I replaced them. The oil pan seemed to have a leak so I pulled it and found that the oil pan gasket was bad. I thought I had a rear main leak but that seems to be one of the only parts that wasn't leaking. The transfer case seal where the transmission shaft goes in was shot and had to be replaced. So, I replaced that transfer case seal and the other seals. The transfer case did not need to be rebuilt.

In order to get the oil pan off the engine I had to drop the passenger side differential shaft. I needed to do that anyways because the axle seals were bad on the driver's and passenger side. The passenger side CV shaft was cracked at the differential and at the wheel hub. I replaced both of the CV axles. The fuel lines were absolutely dust. So I replaced them. The gas tank was leaking so I replaced it. Since I had it out I went ahead and replaced the sending unit and pump. The throttle body was covered in oil from one of the valve cover seal leaks. Took the TBI off and rebuilt it and cleaned it. The IAC valve was stuck halfway down so I replaced it. Since I had the throttle body apart I went ahead and replaced the throttle position sensor. I kept the old one just in case.

It sounds like a absolute Parts Canon however I was pretty much replacing worn out parts that needed to be replaced anyways. If I took something apart and there was a piece I could replace or renew, I did it. The truck had the original R12 AC system on it. I replaced the entire air conditioning system except for the evaporator. I also replaced the water pump because I had the entire front of the engine apart. I also replace the alternator and the thermostat. The previous owner used a much cooler thermostat than oem.

 

[BoondocK5]

In my younger days I seem to remember having to take a basturd file to the bottom of a few TBI throttle bodies. They do like to warp over time. It will give you the screwiest vacuum leak you’ve ever experienced.
You have to initially find it by spraying carb cleaner at it while it’s running and paying attention to the RPM change

 

[ZombieK5]

In my younger days I seem to remember having to take a basturd file to the bottom of a few TBI throttle bodies. They do like to warp over time. It will give you the screwiest vacuum leak you’ve ever experienced.
You have to initially find it by spraying carb cleaner at it while it’s running and paying attention to the RPM change

I picked up a can of carb cleaner about 30 minutes ago. I'm going to give that a shot tomorrow.

 

[Wes Harden]

The 2 ground wires near T stat are in good condition and have a nice clean connection ?

How is the ECT plug and wires ? Bad ECT will give you weird drivability issues

 

[ZombieK5]

The 2 ground wires near T stat are in good condition and have a nice clean connection ?

How is the ECT plug and wires ? Bad ECT will give you weird drivability issues

I sanded all the surfaces clean of corrosion for the ground wires. The ECT plug and wire seem fine but I didn't close the inspect them. I'll give them a look over tomorrow.