Greetings, I have a 99 f150 with the 4.6 V8 that's starting to have a weird issue that finally left me stranded for half an hour yesterday. It all started last summer but has been so intermittent. There's been a few times I get into the truck to leave the house and turn the key to start it and it fails to start the first time, recycling the key and giving it a few seconds it's generally started right up. Now lately sometimes it wont start all the way and will idle so low ...below 1 on the tach so maybe 300/400 rpm, it's a horrible rough idle almost like dieseling. Again, generally recycling the key and waiting a few seconds would fix it. Yesterday, I ran around the city for a few hours stopping here and there with no issues. I decided I'd get me a cigar to enjoy the night and stopped by the shop, I was in there for about 20 minutes; I got into the truck and turned the key and all it did was crank the engine over and over ..nothing. I keep trying to start it every now and then for about 15 minutes and sometimes it acting like it wanted to start but with that low really rough idle ( around 300-400) like a dieseling motor with no response to the pedal. I cycled the key so many times ..lol and it either cranked over and over with nothing or catching that really low Idle but eventually die. I'm in texas so it was hot asf so I went back into the store to cool off and get some water and called a friend for a lift. I was in the store about half an hour, I came back out and decided to try it again and the damn thing started right back up like nothing was wrong at all. I drove it back home without any issues, parked it and turned it off in my driveway. I tried to start it again and it did the same thing and wouldn't start or idle really low. I tried again several hours later and it started fine and again this morning and it starts fine. The truck was my dads and he never did anything other than the typical oil,air filters and breaks etc. So when I got the truck two years ago it developed a miss in it so I changed the original plugs, wires and replaced both coil packs with duralast ones. It fixed the miss / backfire acceleration issues and I hadn't had any issues until whatever's happening now. I did some research and some people say the fuel pump is bad, some say a relay or crank sensor. Right now the trunk will start fine in my driveway and if I cycle the key and don't start it I can hear the pump for a second like they say you should, I don't know if that was happening yesterday because I didn't know to check. Also, there no check engine light on and I put my code scanner on it and it scans it fine and says there's no codes at all. I'm at a loss on this.

 

I'm betting the crank position sensor.

 

Get the codes checked. Borrow a gauge and check the fuel pressure.

When my 02 intermittently failed to start but cranked over, I got a P1000 code which is caused by disconnecting the battery, erasing codes, or no power to the PCM. Since the first two had not happened, and on the advice of a member, I replaced the PCM power relay and that fixed it. But, if yours tries to start and idles low, that probably is not your problem. Sounds like yours is related to getting up to normal operating temperature so I'd suspect something electronic.

 

There's no codes to check nor any check engine light has been thrown.

 

When it idles slow and rough, does it respond if you give it some gas? If so, your IAC is probably dirty and sticking. If this is the case, it should start if you give it a little gas.

 

It's hard for me to even call it a idle ...it's so low but no at least last time when it was in this stage it didn't respond to me pushing the gas pedal nor do I think it has in the past either but in the past it always recovered by cycling the key a few times. This last time it wouldn't even try to fire or start most of the time and when it did it started that low idle. After sitting for awhile it acting like a brand new truck and fired and ran great..I drove it home on the highway without issues.