Idles like it's cammed

[Aaron Powell]

You can test it without engine running, but key on, its air temp, so a few degrees less than outside temp because its "in the shade", lol

Use same scale and voltage as ECT sensor, if memory serves

Is it possible that a bad O2 sensor or small exhaust leak cause this big of a problem?

 

[RonD]

For variable idle, I would say just the PCV Valve, as it can open and close
Regular vacuum leak wouldn't vary
And a vacuum solenoid leak wouldn't either

And can't see O2 or exhaust leak causing it either, nothing variable there

 

[Aaron Powell]

For variable idle, I would say just the PCV Valve, as it can open and close
Regular vacuum leak wouldn't vary
And a vacuum solenoid leak wouldn't either

And can't see O2 or exhaust leak causing it either, nothing variable there

I've replaced the PCV and even blocked it off and still have the same issue. I replaced the dizzy and PCM and no difference (the dizzy was corroded internally due to the truck living near the ocean for so long before I got it). I think I'm just going to go back to stock and see if the issue resolves itself.

 

[Aaron Powell]

For variable idle, I would say just the PCV Valve, as it can open and close
Regular vacuum leak wouldn't vary
And a vacuum solenoid leak wouldn't either

And can't see O2 or exhaust leak causing it either, nothing variable there

Would a faulty TPS cause the fuel cut/fluctuating idle?

 

[RonD]

No I can't see it doing that, TPS is there to give faster throttle response, as MAFs and MAPs are too slow to give instant throttle response
TPS also saves on gas, i.e. when you take your foot off the gas pedal the computer can turn off fuel injectors while coasting until RPMs are under 1,500 or so

Now IF(big if)..............your TPS voltage was fluctuating, not steady, then computer might "think" your foot was tapping gas pedal so would change fuel mix, extreme long shot but not a no shot

You can pierce the center wire on the TPS with a sewing needle and test the voltage the computer "sees"
Steady and under 1volt at idle, .69-.99 volt is spec

 

[Aaron Powell]

No I can't see it doing that, TPS is there to give faster throttle response, as MAFs and MAPs are too slow to give instant throttle response
TPS also saves on gas, i.e. when you take your foot off the gas pedal the computer can turn off fuel injectors while coasting until RPMs are under 1,500 or so

Now IF(big if)..............your TPS voltage was fluctuating, not steady, then computer might "think" your foot was tapping gas pedal so would change fuel mix, extreme long shot but not a no shot

You can pierce the center wire on the TPS with a sewing needle and test the voltage the computer "sees"
Steady and under 1volt at idle, .69-.99 volt is spec

There are times I notice with my foot off the throttle coasting down hill in gear (5 speed manual) that sometimes it feels like the fuel gets completely cut off then cycles back on and then off again. I can hear it in the engine sound and feel the excess drag, then less drag. If that makes any sense

 

[Aaron Powell]

Another thing, during acceleration on initial take off, if I don't float the clutch about halfway engaged and keep the RPMS up, it'll go down to a low idle RPM and climb to about 1k the I feel it kick in and she'll accelerate no problem.

 

[Aaron Powell]

No I can't see it doing that, TPS is there to give faster throttle response, as MAFs and MAPs are too slow to give instant throttle response
TPS also saves on gas, i.e. when you take your foot off the gas pedal the computer can turn off fuel injectors while coasting until RPMs are under 1,500 or so

Now IF(big if)..............your TPS voltage was fluctuating, not steady, then computer might "think" your foot was tapping gas pedal so would change fuel mix, extreme long shot but not a no shot

You can pierce the center wire on the TPS with a sewing needle and test the voltage the computer "sees"
Steady and under 1volt at idle, .69-.99 volt is spec

So I proved the center wire on the TPS connector KOER and had 1.4v to ground. I adjusted the idle screw to allow the butterfly to close more until it no longer touched the throttle cable bracket and got the voltage down to 1.2v out to ground. It's got 5.3v in and at WOT I have 4.3v out to ground. I'm going to warranty out the TPS to see if the one I have is just a little off. If it doesn't change, I'll try and been the tab on the TV that goes into the TPS to try and "close" the throttle plate more to bring the voltage down some more.

After bringing the voltage down that little bit, it seems to smooth out the idle a little faster, but still stumbles and wants to die when I turn the engine off and then back on again.

With the MAF disconnected, in cold start up, it revs to about 1,500k and then drops to 1k and slowly lowers back to normal idle during it's warm up. With the MAF connected, it does not idle up that high, only to about 1k then back down to 3-400 and stumbles.

 

[RonD]

On some 3rd party TPS you may have to elongate the bolt holes to you can adjust the TPS voltage

The anti-diesel screw(fuel injection can NOT have/use an idle screw, no Jets) should be reset
Warm up engine fully, 5min or so
let it idle
Unplug the IAC Valve, engine will stall most likely, if you have adjusted the anti-diesel screw to low
Turn it 1 full turn clockwise(tighten)
Restart engine
You want the engine to barely idle at about 600rpms on a 4cyl with IAC Valve unplugged
So reset anti-diesel screw for that
Plug IAC Valve back in and idle should go up to 750rpm or so

You CAN use anti-diesel screw to fine tune TPS, thats FINE TUNE
So if it was 1volt you can back it off to get .99
or if it was .6, you could tighten to get .7

But you should also have 4.5-4.8volts at WOT
This is where elongating the holes comes in, gives you better control to get the voltage you need

Your meter is reading a little high, so factor that in, TPS and most other sensors share the same 5volt power supply in the computer
Voltage you want are all based on 5.0volt, so if meter shows input voltage at 5.2v, then 1.2 on center wire would be 1.0, - .2 from 1.2, so you want just a bit more down, 1.19 on your meter

 

[Aaron Powell]

On some 3rd party TPS you may have to elongate the bolt holes to you can adjust the TPS voltage

The anti-diesel screw(fuel injection can NOT have/use an idle screw, no Jets) should be reset
Warm up engine fully, 5min or so
let it idle
Unplug the IAC Valve, engine will stall most likely, if you have adjusted the anti-diesel screw to low
Turn it 1 full turn clockwise(tighten)
Restart engine
You want the engine to barely idle at about 600rpms on a 4cyl with IAC Valve unplugged
So reset anti-diesel screw for that
Plug IAC Valve back in and idle should go up to 750rpm or so

You CAN use anti-diesel screw to fine tune TPS, thats FINE TUNE
So if it was 1volt you can back it off to get .99
or if it was .6, you could tighten to get .7

But you should also have 4.5-4.8volts at WOT
This is where elongating the holes comes in, gives you better control to get the voltage you need

Your meter is reading a little high, so factor that in, TPS and most other sensors share the same 5volt power supply in the computer
Voltage you want are all based on 5.0volt, so if meter shows input voltage at 5.2v, then 1.2 on center wire would be 1.0, - .2 from 1.2, so you want just a bit more down, 1.19 on your meter

So the adjustment screw in the throttle body that controls how far the butterfly is open/closed with the throttle pedal not pressed is called the anti-diesel screw? I just learned something new. I was thinking about elongating the screw holes. As you mentioned, I did not take into account the voltage difference with my volt meter. I'll look more into tomorrow after work. I'll keep you posted. Thanks for all your help thus far RonD. You're amazing and I'm learning so much from you. It really is appreciated.

 

[Aaron Powell]

No I can't see it doing that, TPS is there to give faster throttle response, as MAFs and MAPs are too slow to give instant throttle response
TPS also saves on gas, i.e. when you take your foot off the gas pedal the computer can turn off fuel injectors while coasting until RPMs are under 1,500 or so

Now IF(big if)..............your TPS voltage was fluctuating, not steady, then computer might "think" your foot was tapping gas pedal so would change fuel mix, extreme long shot but not a no shot

You can pierce the center wire on the TPS with a sewing needle and test the voltage the computer "sees"
Steady and under 1volt at idle, .69-.99 volt is spec

Could an over voltage cause the issue I'm having? I'm getting 14+vdc at the MAF and same voltage at the battery with the alternator/engine running.

 

[Aaron Powell]

14+vdc seems kinda high. Generally they run in the 13+vdc range.

 

[RonD]

No, thats normal

Just after startup battery voltage should be 14.4-14.8volts, this is a "fast recharge" in case engine stalls and you have to use battery again
After 5 minutes or so it will drop under 14 volts, 13.4-13.8volts and stay there until next start up

Sensors all use a regulated power supply, like 5 volts, so it doesn't vary with system voltage(engine running voltage)
What you are testing on MAF sensors is its Heater, not the sensor, heater is not voltage sensitive

Battery is only used to start an engine, after that the alternator supplies ALL the voltage, 13.5v average, battery is only 12.3v to 12.8v so alternator voltage goes TO the battery to keep it charged up for the next start up

All the sensors use a reference circuit, so what is used is a comparison voltage, a voltage difference, not that actual voltage
If computer sends 5.0v and gets back 3.0v the 2.0v difference is used, not the 3.0v
Now if computer sends out 4.8v and gets back 2.8v then sensor reading is exactly the same, 2.0v difference, this allows for "graceful aging" of equipment, lol

 

[Aaron Powell]

No, thats normal

Just after startup battery voltage should be 14.4-14.8volts, this is a "fast recharge" in case engine stalls and you have to use battery again
After 5 minutes or so it will drop under 14 volts, 13.4-13.8volts and stay there until next start up

Sensors all use a regulated power supply, like 5 volts, so it doesn't vary with system voltage(engine running voltage)
What you are testing on MAF sensors is its Heater, not the sensor, heater is not voltage sensitive

Battery is only used to start an engine, after that the alternator supplies ALL the voltage, 13.5v average, battery is only 12.3v to 12.8v so alternator voltage goes TO the battery to keep it charged up for the next start up

All the sensors use a reference circuit, so what is used is a comparison voltage, a voltage difference, not that actual voltage
If computer sends 5.0v and gets back 3.0v the 2.0v difference is used, not the 3.0v
Now if computer sends out 4.8v and gets back 2.8v then sensor reading is exactly the same, 2.0v difference, this allows for "graceful aging" of equipment, lol

So I've done testing and finally decided to do a compression test and cylinder leak test. Yay, #5 cylinder exhaust valve is bad. 75lbs compression and only holds 10psi air on a leak test.

I've got new valves, new lifters and new push rods ready to go. I'm just having issues finding MLS head gaskets for it. That's what's currently on it, and that's my preference. Would you happen to know if I can use the MLS head gasket from a newer model 3.0?