Dying At Idle

[Fast2500Ak]

My engine (LQ4) usually idles around 500rpm. It does so fairly smoothly. But just today though it started intermittently dying when I come to a stop, or when I shift from park to drive. Especially when the truck has been off for a while, or has been sitting at a long stop light. Once I get about 1500 RPM the engine runs flawlessly, but as soon as it drops it seems to cut out, then start, then cut out, and so on; and if I give it gas it does not get going until it resumes from cutting out and it surges. The surges are about a second apart.

 

The idle just seems to bog a few times then give up and stall. No check engine lights have been thrown.

 

I have concluded several causes:

 

1) last night I got some gas. I don't particularly trust this Holiday station, but my favorite chevron was just torn down. This was immediately before the incident started and it was a fill from close to empty.

(Bad gas: clogged filter, injectors, poor combustion)

 

2) Recently my battery (few year old opt. red top) has been discharged a number of times, three involved bad judgment and me using the battery to run the radio while in the garage while aligning the lights I installed behind the grill, three were a result of cold, one was a result of console lights being left on while out in the cold. On this last time the battery refused to start on my newer trickle charger and needed to be left at full start position for about 15 min on my older one, and really didn't want to take a charge back, but did eventually. The -40 degree + weather has killed it multiple times before this and it's always bounced right back.

(Not enough amps? is that a possible cause?)

 

3) About a week ago I noticed the alternator is making a hissing sort of sound, I guess it might be a bering or something

(When the rpms go up, the engine returns to normal, so I don't think this is the problem, just seemed a bit odd.)

 

4) It could also be a TPS sensor, I think 00-02 has had some problems with those

(A friend of mine told me this a while back, but I'm not sure if its accurate)

 

5) something interfering with the pcm

(not sure what that could be... ground maybe)

 

I clean my: throttle body, MAF, air filter, ect... regularly. this afternoon I put in two bottles of HEET and three cans of Seafoam, and drove around

for a while. It returned to normal. Then when I was about to leave a friends house after sitting for a while it started doing it again. It seems like after a while of driving it gets better. So I'm leaning towards alternator or the battery. also the volts jump around a bit right before she dies, the other gauges are completely normal.

 

What do you guys think?

 

Thanks in advance for the input, and sorry for the long post. I have to drive the 399 mile trip through the middle of nowhere back up to UAF in Fairbanks on Tuesday and I'd like to have the piece of mind of at least knowing what is causing this.

[Fast2500Ak]

This morning it threw a code for low MAF circuit. I pulled the plug on the sensor and the truck stopped dying, it actually seemed to be running better. I just cleaned the sensor and its connector, and have the battery disconnected. Also I had the battery tested, it seems ok.

 

any suggestions?

Edited January 20, 2008 by Fast2500Ak (see edit history)

[Fireman31]

your MAF was most likely dirty, cleaning it should cure the problem, also consider running a can of SeaFoam through your next tank

[Fast2500Ak]

I did run seafoam and I clean the MAF regularly. Both of those were good suggestions though. I ended up flying back to college, I got about 40 miles out of wasilla by that time the engine was kicking on and off even at high rpm making the truck buck violently. Needless to say I decided it was a bad idea to try and make it go a few hundred more miles like that in a white out, that and a friend of mine who went ahead called and said there was a foot of snow on the road near cantwell and the highway was closed at peters creek. When I was in Wasilla I went to napa, rirped out the alternator and had it tested, it checked out fine. Its at the dealership now, I got to frustrated trying to riddle it out and its

 

When I unhook the MAF the the idle characteristics stay about the same, how often do MAF sensors go bad?

[yttaf]

I'd have to guess the battery until the maf code showed up. I had a similar problem where it would die when coming to a stop or change from park to drive, a new battery fixed it for me, but I never threw any codes. My volt gauge would drop to around 11 or 12V right before it would die.

Edited January 24, 2008 by yttaf (see edit history)

[Fast2500Ak]

I'd have to guess the battery until the maf code showed up. I had a similar problem where it would die when coming to a stop or change from park to drive, a new battery fixed it for me, but I never threw any codes. My volt gauge would drop to around 11 or 12V right before it would die.

 

Mine did that too, but when I had the battery tested it passed. The guy said it was only slightly low on charge but within reason, not so sure I trust that now. This problem sure seems like an electrical problem at any rate, because when the engine is running, it can seem fine for awhile, sometimes for ten minutes or so, then just starts dying out of the blue, the rpms drop, then the engine slams back to life and nearly jerks the wheels off the rotors, kind of like the engine has narcoleptcey. Then it sometimes goes away again and then comes back, catches me off guard, not fun on ice.

Edited January 24, 2008 by Fast2500Ak (see edit history)

[Blaker888]

I could be sayin somethin stupid could ur MAF be bad I know if u touch the little spings or wires inside it tends to make them go bad. I also had a Slp intake that didnt fit to well and the tube would suck air before the MAF and would make the engine run all crazy like u said the RPms would want drop and Id try to give a little gas and the Rpms would jump and truck would jump like Five feet just some ideas

 

Mine did that too, but when I had the battery tested it passed. The guy said it was only slightly low on charge but within reason, not so sure I trust that now. This problem sure seems like an electrical problem at any rate, because when the engine is running, it can seem fine for awhile, sometimes for ten minutes or so, then just starts dying out of the blue, the rpms drop, then the engine slams back to life and nearly jerks the wheels off the rotors, kind of like the engine has narcoleptcey. Then it sometimes goes away again and then comes back, catches me off guard, not fun on ice.

[Fast2500Ak]

I could be sayin somethin stupid could ur MAF be bad I know if u touch the little spings or wires inside it tends to make them go bad. I also had a Slp intake that didnt fit to well and the tube would suck air before the MAF and would make the engine run all crazy like u said the RPms would want drop and Id try to give a little gas and the Rpms would jump and truck would jump like Five feet just some ideas

 

 

Well that is exactly right, the MAF had failed. That was causing the dying at idle, but the high rpm stalling was the result of a dying fuel pump. That was why it was hard to pin-point the problem as it had compounded itself. Shop just got done replacing units.

 

Thanks again for all the input

Edited January 26, 2008 by Fast2500Ak (see edit history)