im working on my inlaws 2000 lesabre l36, 60-70k miles most parts original. it wouldnt start yesterday, so we let it sit over night still wont start, then i put the throttle 3/4 to all the way down and it started and ran rough. i checked tps through the live data seems fine, maf, temp, and fuel pressure seem fine. he said it has been hard to start for a while and once started runs and starts fine. and now that has started it will start without the throttle pushed every time.

It could very well be the IAC. Probably not opening all the way, or the opening is getting gummed up.

But, to do the throttle plate test, it only involves cracking it open a tad bit. Basically, 5%TPS output on your scanner/laptop. If you go 3/4 or more(depending on platform) you could force the PCM into "clear flood mode" which shuts the injectors off during cranking.

Another possibility is, the dreaded coolant leak. When the engine cools down, coolant leaks past the crappy gaskets and into the cylinders. Not enough to hydrolock, but enough to wet the plugs or foul the fuel mixture causing a hard start.

Also check to make sure the Fuel Pressure Regulator isn't leaking. It'* another common failure point. Just pop the vacuum line off of it. If fuel come out, it'* bad.

kinda what i was thinking , gunna have to wait and see and try just giving it a little throttle when it wont start again. i forgot to add i looked at cyl three plug when it wasent starting, at least that one didnt look like coolant, just smelled like gas and had good spark. could be leaking diff cyl but hopefully not.

i did leave the gauge on the rail while i was looking at stuff, pressure seems fine

Gasket leaks are racial, they'll pick whatever cylinder to leak into. You would have to pull every single plug. But that can be avoided just by checking the coolant level.

I think Randall was talking about the FPR being bad and sucking gas via the FPR vac line back to the TB. FPR can still show a decent psi when running, but may leak past once vacuum is gone. They can be funny like that sometimes.

coolant level is good, checked fpr as well. but it started again without the throttle.

Now that the weather is changing, that brings to mind water in the fuel through condensation. Maybe get a bottle of MACs fuel treatment in the yellow bottle from NAPA. It'* better than a lot of the other water evaporators on the market. At least you can eliminate that possibility.

I might add that the MACs product mentioned is not isopropyl alcohol like most other products. It would be a good maintenance additive to use in the fall anyway.

not sure where he gets his gas, but he drives 45miles each way to work so he has got to use at least a tank a week and he said its been getting progressively worse. we couldnt get it to not start so i had him drive it home, and told him when he goes to work tomorrow just try to start it by putting the gas down a little bit.

Did you apply vacuum to the FPR? Ive seen where you need to stretch the diaphragm to get it to leak fuel.