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Discussion Starter · #1 ·
Fighting a low rough idle, that has progressed to stalling.

A few weeks back we have changed the plugs, wires, coils. Cleaned the throttle body and idle air control. New front O2 sensors. And today changed the MAF. Still not running right and getting worse. No codes thrown.

Connected my obd module and ran my copy of dash command, reading live while the truck was running. The throttle trims were bouncing, and the O2 reading were bouncing while the truck ran rough. When it warmed up, the trims leveled out and o2 was steady.

Always run on super unleaded.

Any advice?
 

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Your description sounds like a bad idle control valve / idle bypass valve.
 

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Fighting a low rough idle, that has progressed to stalling.

The throttle trims were bouncing, and the O2 reading were bouncing while the truck ran rough. When it warmed up, the trims leveled out and o2 was steady.
Is this issue just when cold? Ending of post seems to indicate no rough running when warmed up.
......
 

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Discussion Starter · #4 ·
Yes, the issue had been going away when warm, but is now continuing after warmed up.

Suggestions on testing the idle air valve. Was gummed and sticky before i cleaned it, now the barrel inside moves freely. Does this run on 12 volts?
 

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Discussion Starter · #6 ·
Tested the valve with 12 volts. It clicked and moved as I expected. I reinstalled and started the engine.

It did as usual, ran at about 1200 rpm for about 30 seconds or so, then started to drop and then stumble. I unplugged the idle air valve, and it dropped to a few hundred rpm, plugged it back in and it idled most normal.

My thoughts are the valve is possibly going bad?
 

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Your description sounds like a bad idle control valve / idle bypass valve.
Ha ha! Point for my team? Cleaning may or may not fix it. Try to pick up a replacement, scan and clear codes. Should be all good if no other system lean or system rich codes.
Let us know how it turns out.
 

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Suppose it could be the valve. I prefer to troubleshoot if possible prior to shotgunning parts. Are you using the workshop manual? If not there's a good bit of info there that may help. Bad IACV should give code.
.....
 

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Discussion Starter · #9 ·
Gone through the manual sensor by sensor.

Not the idle air valve, throttle position, fuel pump, spark plugs, MAF. Put fresh gas in. No air leaks.

Still runs like crap after it warms up.

No codes are showing.

Realtime readings show the fuel trims bouncing and the o2 voltage bouncing from .05 up to .70 volts up and down.

Bad o2 sensors in the batch?
 

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Discussion Starter · #11 ·
Changed rear o2's again, ran great while it was 70 degrees out.

Back to 45 today, runs like crap. Changed spark plugs, again. Nothing.

No codes. Coughs and stalls still. Ready to drop it at the junk yard.
 

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No fault codes? Even after running crappy? Sounded like you were on track with the idle air control valve or air flow sensor... Sorry to ask but How did you get on to it being a 02 sensor?
 

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Man, I sympathize!

If there are no vacuum leaks, I would revisit the MAF.
It seems that these MAF units are sensitive and often fail after a cleaning.

Your observation that the truck runs better with the MAF disconnected often indicates a failed MAF.
 

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Discussion Starter · #15 ·
I've tried 3 different maf's. 2 used one new. No different.

On the path of coolant sensors.

Top one unplugged, immediately makes it run bad. Scanner shows -40, o2 runs solid full rich. Attempting to change for new sensor.

Can't find a lower sensor. Not on the radiator. 99 d2 has no lower sensor?
 

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How did you get on to coolant temp sensor? Pretty sure ther is only 1 on a 99 (top centre of the intake) again. Any codes set? There must be.
Maybe time to get back to basics, step back and think it out.
 

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Discussion Starter · #18 ·
Coolant sensor was the magic bullet.

Gauge worked, scanner read the temp, but after installing the new sender, the gauge read up to temp twice as fast.

Happy truck now
 
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