Won't run without gas

[monteburns]

Now, before you lay into me with the "just give it gas you dolt" comments, hear me out:

2000 LC, 118k miles
A couple of times in the past year or so the LC would crank but not start but then the issue would disappear and it would run without a hint of an issue.

Well, now it won't start unless I push the gas pedal. It's hard to get it to turn over, but when it does, here's what happens:

1. If I let off the gas quickly, it will die.
2. If I let if off slowly, then may die, but will idle between 200 and 500 RPMs.
3. When I hold the gas pedal down above 1k RPMs, it sounds smooth and seems to run fine.
4. There is a strong exhaust smell-smells rich like an old Chevy engine-weird smell.
5. Behaves like this consistently, no codes, no CEL, no dash indicators at all. We ran the engine to get it warm to see if it would throw any codes, but nothing.

What we've done to no avail:
1. Replaced fuel pump
2. swapped the EFI fuse
3. swapped the EFI relay
4. Timing belt was done 18 months ago, but all harnesses seem to be clear from obstruction from what I can tell.
5. No key immobilizer issues. I don't even have a red blinking security light. LC starts with a non-transponder after-market key.
6. Opened the air box when trying to start, no change.

If I can get it to start, I can keep it running and even drive it around.

At this point I'm stumped. Any help is greatly appreciated.

 

[ihadmail]

Are there any CEL codes?

Tried cleaning your MAF sensor?
Tried cleaning your throttle body?
Throttle position sensor bad maybe?
Read the thread about "APPS" going bad?

 

[reznunt]

TPS maybe

 

[re_guderian]

Also search about the engine compartment fuse/relay block replacement.

 

[LBridges]

Under the engine category in the diagnostic section of the factory manual there is a section about the starter signal circuit, which influences fuel delivery on start-up. Might want to give that section a look.

 

[aljollano]

TPS maybe

X2.

A.J

 

[2001LC]

"4. There is a strong exhaust smell-smells rich like an old Chevy engine-weird smell"

Is this like raw gasoline smell?

 

[Sandroad]

Why does the truck start with an aftermarket non-transponder key? Is there a remote start system installed or has the ignition system been modified?

 

[Dclain87]

I had the exact same thing happen on my Camaro SS. Turned out to be the coolant temp sensor jacking with the air to fuel ratio.

 

[Tahomatom]

My old Heep you do this and it turned out it was a Cat issue. There was a piece loose and if I hit a speed bump just right it would restrict flow. The act of starting would then move the loose partback to its original position and run with no issues and no codes.
Used to have to replace my cats every 18 months or so.

 

[AimCOtaco]

Sounds like airflow to me, clean the TB carefully and be sure the idle air circuits are clear and also check exhaust for restrictions.

 

[TeCKis300]

Sounds like a classic vacuum leak issue. Check for a leak post MAF.

 

[Skidaho]

I had the same symptoms in my '99

I cleaned the throttle body and the problem went away. Been over 2 years and still no problems.

Hope yours turn out to be that simple.

 

[monteburns]

Are there any CEL codes?

Tried cleaning your MAF sensor?
Tried cleaning your throttle body?
Throttle position sensor bad maybe?
Read the thread about "APPS" going bad?

Thanks for all the replies. I'll start by cleaning the MAF and the throttle body. Funny that this just happened overnight really. One day running fine, next day it starts acting up.

 

[monteburns]

OK, we found the culprit. All you guys that said throttle body were correct. Frankly, for me it's almost never been that simple, but I'm happy in this case that it was. The LC runs with much more pep and feels lighter on it's feet than before. Thanks to everyone for chiming in-love this community.