99 Lesabre intermittent hard start
 

Hello all, I have a 99 Lesabre 3800 with 207k on it. Recently started intermittently starting hard. Cranks for about 10 secs then fires up. Engine speed seems to sputter for 20-30 secs after the start as if starved for fuel, then evens out. This is only when it starts hard. Other times complete opposite, fires up immediately. Flick of the key and boom its running. Seems to always be either one of the two but no pattern detected. Not effected by temp or time at rest. Same result whether sitting for 5 mins or overnight. Always runs just fine once it starts and never has stalled. I apologize in advance if there's too much background info but replaced intake/gasket, valve cover gaskets this summer, fuel pump and sending unit summer 2013, fuel filter summer 2012. I replaced GMs plastic quick connect fuel lines with high pressure rubber lines and clamps from the filter to pump. It doesn't leak but I believe it caused my PO440 code that comes and goes. Also, although I have never felt it misfire while driving, it recently threw a cyl. 2 misfire code. I did check the vacuum line on the pressure regulator for traces of fuel but no luck. Waiting for day off to diagnose but need a starting point and your advice is appreciated! Thanks!

Next time you expect it to happen, hold the throttle open JUST A TAD. Basically, we are cracking the butterfly plate open just a little bit. Now try and start it. If it starts right up, let off. If it stalls, repeat the process.

If it does do this, remove and clean the IAC valve. As time goes by, the IAC gets clogged up with carbon preventing startup.

probably due for plugs and wires. and check the coil terminals and the pins under them for corrosion

You replaced your plastic fuel lines with rubber? If they weren't leaking, why?

Those lines have nothing to do with P0440....

Why did you replace the fuel pump a year ago? What brand did you use?

It sounds like you are describing cold starts... but if the problem occurs on warm starts (i.e. engine won't start back up after it was running for awhile, and you shut off for a few minutes) then it may be a failing Fuel Pressure Regulator. You may have already checked that if you replaced all the vacuum line described, since it (the FPR) is connected to one end of those lines by the throttle body.

@ Mike1995, thanks I'll give that a shot. I'll also check plugs, coils and wires. I have a hunch its more a fuel or throttle issue than spark though. I pulled all plugs a couple months back to compression test and they looked ok. @ Tech II I replaced them with rubber because I damaged the quick connect fittings while disassembling and was it was much cheaper and more available to go rubber lines. Not sure now about brand of pump. Probably a Napa house brand.

75 to 80 percent of the time single cylinder misfire is spark related.3800's are not picky on fuel and since you said it does it when its only been off a couple minutes thats not normally a fpr issue, though its easy enough to throw a pressure gauge on and see if the pressure is going away that quick(then you know it is the FPR). good test to do is get a fine mist water bottle and start the engine. mist the wires and coil area and if you see arcing or hear the engine change there is your problem.

@ Mike1995 your tip led me somewhere. I cracked the throttle and cranked and it fired right up for 1 sec then sputtered out. Tried again and started and ran. Never did that before so Ill clean IAC valve. thank you for the lead. Also I missed one of your questions @Tech ll . I replaced fuel pump because integrated lines on the sending unit were rusted and leaking from Minnesota winters.