99 LC dies randomly. Pls help.

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The unresponsive nature of the throttle pedal would have me looking closely at the APPS and TPS.
 
When you get your OBD2 app connected and monitoring, include the throttle position sensor.

Also, when the engine RPM slowed down to 1200RPM while driving at 50mph, did the truck violently slow down to match engine speed to driveline speed through the tranny? Or did the driveline disengage from the engine during this event?

It was coasting and slowing down, just as though I had let off the gas.
 
The unresponsive nature of the throttle pedal would have me looking closely at the APPS and TPS.

The throttle body is new-ish though (I don't know how many miles on it but it certainly looks new) and I would guess that the APPS and TPS are new as well. It doesn't seem to make sense that you would buy a new throttle body and reuse old sensors. Also, no codes at all and it seems to me from my research that those throw a CEL code, do they not?
 
The throttle body is new-ish though (I don't know how many miles on it but it certainly looks new) and I would guess that the APPS and TPS are new as well. It doesn't seem to make sense that you would buy a new throttle body and reuse old sensors. Also, no codes at all and it seems to me from my research that those throw a CEL code, do they not?

My APPS went out recently. It threw a CEL and truck never died when driving. Always stayed on just no throttle. Your issue doesn’t sound the same as my experience with APPS.
 
My 2001 LX would stumble & go dead after letting my foot off the gas going downhills or at stop sign. My problem ended up being the previous owner had replaced the MAF with one a cheap auto parts MAF. The auto parts MAF was slow to respond. Here was my thread:

 
My 2001 LX would stumble & go dead after letting my foot off the gas going downhills or at stop sign. My problem ended up being the previous owner had replaced the MAF with one a cheap auto parts MAF. The auto parts MAF was slow to respond. Here was my thread:


Thanks for that. I cleaned the MAF but maybe I should replace it. I believe mine is an OEM part but not sure. I'll have to take a look later.
 
You are welcome and if your MAF has never been replaced, I would advise you to replace it anyway. Because it is now +20 years old and +200k miles.
 
You are welcome and if your MAF has never been replaced, I would advise you to replace it anyway. Because it is now +20 years old and +200k miles.

Yeah I might just do that if the EFI relay doesn't do it. My Bluetooth OBDII thing should be here tomorrow, so maybe I'll get around to figuring that out this weekend and be able to get some more information.
 
Bluetooth OBD plug is all set up and good to go. Now I just need it to die again and see if I get any weird readings I guess.
 
A couple of years ago I was on a trip from Los Angeles to the Wind River area of Wyoming. The same thing happened to me. I'd had everything checked out by a trusted LC mechanic. A month before I had the serpentine belt replaced. It turned out it was the belt rubbing against the timing wire and causing intermittent shorts that got worse. You can't see it because its behind the cover.
 
A couple of years ago I was on a trip from Los Angeles to the Wind River area of Wyoming. The same thing happened to me. I'd had everything checked out by a trusted LC mechanic. A month before I had the serpentine belt replaced. It turned out it was the belt rubbing against the timing wire and causing intermittent shorts that got worse. You can't see it because its behind the cover.

Do you by chance have a picture? I should be able to see it as I don't have a cover (PO had taken it off and I chucked it, I hate those things).

I've looked at everything that I can see to check for this, but maybe I missed it.
 
It hasn't died in a week now. New EFI relay showed up today and I put it in there.
 
It hasn't died in a week now. New EFI relay showed up today and I put it in there.
Do you have a part number for the relay & where you purchased it from? I might just change my as a preventive measure.
 
Well I guess the EFI relay wasn't the problem. It died coming to a stop sign yesterday. I thought I could smell gas, just for a second or two. I suppose a new MAF will be my next purchase.

I had OBDMate up on my phone and I didn't see anything out of the ordinary, although my eyes weren't glued to it because driving.
 
Update: it wasn't the MAF either. Nor was it the fuel filter. It was the fuel pump, which finally died for good last week. Back on the road and feeling better.
 

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