Help! 02 LS random stalling

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Broseph

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I spoke with joegr on this some and I'm seeing if anyone else has experienced this issue so I know what to look for next. 02 LS 3.9

Two weeks ago my car died do about 20-25mph after turning onto a street behind my work that has some gradual turns. I've gotten a lean coad P0174, P0171 (I think) for both banks lean for awhile now that would randomly pop up, and my car will idle high after cold start ups for anywher between 30 seconds to a minute before dropping to ~1,000rpms.

With the lean codes, idling, and car dying I figured the pump was weak and needed replacement (i did a pressure test at the rail and the psi would SLOWLY climb after turning igntion and stayed in ~35 range). Bought a new electric motor along with a jet pump (fuel was leaking off immediately after shutting off ignition) and replaced both pumps, including a new filter. Started it up yesterday and it did a little stumbling before figuring out what it liked. Took a short trip around the neighborhood and it was fine

Decided to drive the fiancee to her friends get together downtown - bad idea without doing a good test run by myself.

The car died twice after accelerating and then braking before a light downtown, think 0 to 20 and back to 0 again.

Here's the kicker, no codes come up, I put it in park and the first time it did a couple cranks before starting but the second time it fired right up.

I need some advice on what to look into after this because it's frustrating to figure out without any codes and after doing the other work.

Could it be IACV when it kicks in? At idle the car willl sometimes drop real low- 400rpm or less - and then suddenly jump back up. I don't see how this could have effect while braking at 10mph or higher. Or is it more likely electrical at this point? Just seems unlikely with it starting back up right away

And maybe the most obvious but I'm not sure, is Ford or someone with a nice scan tool able to read something off the PCM that could figure out what the problem is?

Thanks for the help in advance

Just to add, driveability on highway, cruising, stomping it are all fine.
 
Somehow this sounds like it could be a loose electrical connection somewhere. Not much help, I realize.
 
I've thought about this more and more, and it seems a possibility. Most fuel related problems I think people were having issues with hesitation, surging and such before it would die and problems starting.

The sudden dying the being able to restart might be electical, but only when braking or turning seems odd, since it only happens at slow speeds.

All wiring to alternator, battery and grounds are good, I checked those.
 
There is still issues with idling, and the rpms dropping too low then bouncing back up. I unplugged the MAF and it ran awful. Would this leave me with IACV or a vacuum leak?
 
joegr said:
Yes (to both), and maybe TPS.
Click to expand...

Joegr, would a higher idle speed be indicative of TPS?

After replacing the pumps, filter, etc. I noticed the last few trips that after letting off the throttle the RPM's will stay well over the 1,000 range when pulling up to a stop light and will stay high after stopping for a few seconds then drop. I was thinking IACV or TPS since idling rpms will drop and raise and never really stabilize.

Two questions then: Could either one of these cause the stalling I've experienced under the conditions? And, is there a way to test the TPS?

From what I've learned, the IACV is pretty much narrow down other problems (MAF) and if not, then replace IACV since cleaning it won't do much and just charging it with 12v and seeing if it opens means next to nothing since it varies constantly during operation.
 
Yes, but it could also be the IAC or a vacuum leak.
You can disconnect the TPS connector and use an analog ohm meter to test it. As you open and close the throttle, the meter should move smoothly in step with it.
No, there's no good way to test an IAC, unless you have two gen I LSes (just swap parts around).
 
So I got it to happen again on break. If I'm going slow enough 10 -15mph and I tap the accelerator and then hit the brake the rpm's fall flat.

Somewhere around 300 rpm the battery light came on just before dying then after rolling a bit the engine light and others came on....here's the kicker - heater, lights, radio, everything was still running the whole time. Parked and fired it back up. So the battery light coming on is kind of strange with all electronics still working.

Will the battery light come on as the RPM's get real low meaning not enough power is charging system, or is my alternator dying intermittently after hit the gas and brakes right after? Seems like it might be more TPS related, but suggestions are welcomed.
 
Yes, you would expect the alternator light to come on at very low RPMs, even with no alternator fault.

At 10-15 MPH, the throttle is nearly closed and manifold vacuum should be pretty high. Tapping the brake will add some unmetered air to the engine. Normally, it is not enough to cause any issue, but if you have a problem, it can. I don't think this narrows it any from your previous symptoms.
 
I forgot to add, the car tried stalling on the same trip. Same thing happened to where the battery light came on, but since I was paying attention, I was able to tap the accelerator before the car stalled out and it revved back up and the light came off, leading me to believe it is more IACV or TPS than anything else.

So if the throttle is pretty much closed at 10-15mph the IACV takes over for metering the air then correct?

Apologies for my previous posts, I've already corrected brake like five times *idiot*
 
Yes, that does point it a little more towards the IAC. The IAC has full control when you take your foot off the gas pedal.
 
Broseph, I had an IACV go bad in my '99 F-150. You are describing the exact symptoms, except that mine made a little bit of noise at the same time. You might hear this if you pop your hood while it's doing it and that could help you pinpoint it. Immediately after mine was replaced, a friend's Dodge Ram had his IACV go bad and there were similar symptoms. In his case, it was mostly happening until the engine warmed up. Third example was a friend with a ~'98 F-150 crew cab. His did that rev up at the light thing, almost overpowering the brakes.

These valves get carbon buildup and begin to seize up. You can take it apart and clean it, assuming you can access it, and that will usually get you back in business for some period of time, thought they normally go bad again soon. In other words, if the cleaning restores a smooth idle, you know you should replace it.
 
That sounds almost identical!

Thanks, I actually pm'd joegr about doing this last night. I pulled the TPS sensor and started the car to test the voltage at it but the rpms shot up to around 3,000after starting the car so i skipped that. Took off the IACV, it didn't have (too) much carbon build up, I cleaned it and put it back on.

The idle did smooth out, but once it got up to temp i was able to tap the accelerator going real slow then hit the break and it died. Strange why it happens at temp. I got an intake still from my old engine with the IACV, so I'm going to replace it here shortly to see if it works out.

Thanks for the help. I'll post back once I get this sorted.
 
Broseph said:
The idle did smooth out, but once it got up to temp i was able to tap the accelerator going real slow then hit the brAKE and it died. Strange why it happens at temp. I got an intake still from my old engine with the IACV, so I'm going to replace it here shortly to see if it works out.

Thanks for the help. I'll post back once I get this sorted.
Click to expand...

Soooooo.... Let me see if I have this right..... You hit the gas (building up engine vacuum) then immediately hit the brake (taking the vacuum from the engine and giving it to the brake booster) and the engine died?


BTW, sorry for your loss last week.....

iphone-San-Diego-Chargers-Logo.jpg

iphone-San-Diego-Chargers-Logo.jpg
 
I can't catch a BREAK. That's like my 18th typo for that.

But yes, that's correct. I had the driver side cylinder head off this car, replaced timing chains, gaskets, and you name it, yet the whole vacuum concept escapes me.

With that said, I'm not sure what you're getting at.
 
Well played sir...well played.

However, the same outcome would've happened this week regardless of who won.
 
Broseph said:
I can't catch a BREAK. That's like my 18th typo for that.

But yes, that is what's happening. I had the driver side cylinder head off this car, replaced timing chains, gaskets, and you name it, yet the whole vacuum concept escapes me.
Click to expand...


That's because, if I understand the boosted brake system correctly, you're taking engine vacuum (essentially starving the engine) and giving it to the brake system. There should be something to keep that from happening like a check valve somewhere. IIRC, some early LSes had an issue with the brake booster. I know when I had the 2000 if I went from gas quickly to brake the pedal was hard and the brakes took a second or so to bite.
 
Broseph said:
Well played sir...well played.

However, the same outcome would've happened this week regardless of who won.
Click to expand...


Unfortunately, Andy Dalton seems to get flustered too easily. He tends to make poor throwing decisions. Peyton is susceptible to the same problem when playing the Chargers.
 
LS4me said:
That's because, if I understand the boosted brake system correctly, you're taking engine vacuum (essentially starving the engine) and giving it to the brake system. There should be something to keep that from happening like a check valve somewhere. IIRC, some early LSes had an issue with the brake booster. I know when I had the 2000 if I went from gas quickly to brake the pedal was hard and the brakes took a second or so to bite.
Click to expand...

It's interesting that you say that. The brake feel on the car was never great, so i went with stainless braided, and did the Jaguar upgrade up front. It helped, but I remember asking someone about the pedal still having a good amount of give before grabbing. I bleed and bleed the lines so I know there isn't air in them but not much changed.

IIRC, someone said something about removing the tube to the brake booster and blowing through it to see if pressure would build up or not and I came up with nothing.
Is that a correct way to test the check valve or am I supposed to have the ignition on or something?

Again, vacuum isn't my strong suit, but wouldn't this be a problem at any speed when hitting the brakes (throttle plate shut) if there was an issue with the booster?
 
LS4me said:
Unfortunately, Andy Dalton seems to get flustered too easily. He tends to make poor throwing decisions. Peyton is susceptible to the same problem when playing the Chargers.
Click to expand...

If one of the league's worst passing defenses can generate the same pressure this week, then it's anyone's game. Denver's O line has been much better at pass protection than the Bengals, but I agree - if any quarterback gets pressured, most will crumble....it's going to be a good game and I think it will be a lot closer than that terrible display of football last week.
 
So I pulled the hose from the intact. I was able to blow air into the booster, but I could not suck any air out. Everywhere I've read, it is supposed to be the other way around. Is the LS different or is the check valve done?
 
Broseph said:
So I pulled the hose from the intact. I was able to blow air into the booster, but I could not suck any air out. Everywhere I've read, it is supposed to be the other way around. Is the LS different or is the check valve done?
Click to expand...

It's not just a simple check valve. I doubt that you were blowing air into the booster. I suspect that you were blowing air into the intake, where the other port on the valve assembly goes to.
 
Put on IACV from old intake. Still having same issues, so that's out. The TPS seems unlikely but I'll try it tomorrow.

I figured I'd start with the simple items first. I cleaned the MAF a few months back and figured it wouldn't be an issue. But I decided to unplug it and see what I got and it ran okay. Even backed it out the drive way and pulled back in.

When I hit the throttle it wasn't smooth but it didn't buck or do anything crazy, and the idle wasn't bad. This mean the MAF is shot?

Took the filter off and peaked in, sensor looked brand new. Went ahead and cleaned it again and unplugged the battery incase that had something to do with the other IACV being on but I don't think there is a learning period for it. Any advice here on out?
 
Have you checked your hard vacuum lines for breakage/cracking????
 
Yes, I went over those. Not the greatest connectors in the world but they're all on and none are cracked. Can't hear any hissing and I did the carb cleaner check for leaks and came up empty. This is getting frustrating
 
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