My Buick Lesabre has been running horribly the past few days. I noticed it
started to buck while driving after pumping some gas, eventually it stalled
out. Had to put it in neutral while rolling and it started back up. Continuously
would start to buck again and stall. I thought I had got some contaminated
gas so I dumped some high grade fuel cleaner in it and have been filling it
with high octane premium gas, days later the problem still persists. It barely
starts in the morning, have to pepper the gas and maintain a certain RPM
before it will stay and idle or it just instantly stalls out. Ive had the error codes
scanned on it, and I have a few minor EVAP leaks registered but research is
telling me that shouldn’t be causing this kind of issue. I noticed the intake
gasket was loose and tightened it, thinking maybe my fuel was too enriched
with air, hoping that maybe that was the problem. But it is still stalling out. It
has about 148k miles on it, limited edition and has always ran great the
couple years I have had it. Really out of my mind trying to figure this one out.
Symptoms are similar to a failing fuel pump.What year is it?
It is a 2004.
You need to measure fuel pressure to confirm a bad fuel pump.A good independant shop will charge you very $ to perform this test.
It is possible the intake gasket is not doing its job, it may need replacement rather than just tightening.
Do you recall what EVAP codes were pulled?
Tester
Thanks for the replies, everyone. I had them print out the codes for me and they are as follows:
P0442
P0128
P0455
P0442
P0455
Replace the thermostat and fix the LARGE EVAP leak.
Tester
I just have no idea what the large EVAP leak is or how to diagnose it… don’t have the money to take it to a shop to get it checked out, either. Its very odd, my father was just driving it today and said sometimes it ran normal and then it would stall out.
One of the EVAP codes refers to a problem with the purge flow.
If there’s a problem with the purge control valve, the engine will be constantly be drawing fuel vapors from the gas tank, causing a rich condition. And when you refuel, as the gas is dispensed into the gas tank, fuel vapors are forced into the engine. This would then make it hard to start the engine, and the engine would run rough when it did start.
But the P0128 code is the big one. "Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)"
Tester
I own a 2005 Lesabre and a 2005 gmc truck. I’ve had the P0128 code on the Buick, and resolved it by replacing the thermostat. However, I had no driveability issues.
I’ve also had the P0455 code on the GMC truck. I resolved it by replacing the purge valve solenoid. However, I had no driveability issues here either.
The purge valve solenoid is fairly easy to test. Ignition off, it should be closed and you shouldn’t be able to blow air through it. Ignition on, it should be open and you should be able to blow air through it. If I recall correctly. Possibly others can verify. I may be 100 percent backwards, I simply do not remember. Regardless, key on vs key off it should be different. To test it, remove it and apply 12 volts (battery terminals and a wire) to one terminal and ground to the other terminal. Either terminal is fine for pos or ground.
Both of these issues need to be resolved to turn off the cel and remove those codes. But I’m not positive either of those codes are causing your issue. This is why I like to resolve a check engine light / code as soon as it appears. So you’re not chasing rabbits fixing old minor issues when a true driveability issue arises.
If you need further instructions, please let me know. A lot of my tests are shade tree / hack I will admit. But I rarely take my vehicles to a shop unless something needs rebuilt anymore, and I’ve learned a few tricks along the way.
Your issue, to me, sounds more like a throttle body issue. Once the pending codes are resolved, I’d clean the throttle body and idle air control valve. Then clean the MAF sensor.
If that doesn’t do the trick, I would suspect the idle air control valve or the maf sensor as faulty. There are hack tests for the maf sensor as well, but the cause for the current codes needs to be addressed to rule those out.
The purge valve opens only when the engine is started cold.
Because when the engine is started cold, it requires a rich fuel mixture anyway. So the fuel vapors are drawn from the charcoal canister into the engine during a cold start to burn the vapors and to help enrich the fuel mixture.
Tester
Thanks. I wasn’t sure. I remember now mine was failed open. It was open (could blow air through it) with ignition off, so I assume it remained open at all times, yielding the 0455 code. However, the only difference I noticed after replacing it was the check engine light and occasional “tighten gas cap” message went away. I never noticed a performance issue. I was hoping replacing the solenoid would yield 20 more horsepower. Sadly, no… 
Also, OP, if you do shadetree tests, do not used compressed air. I blew in the valve using some rubber hose and my lungs. I do not think the evap system will hold up to compressed air and I believe high psi could damage the system quickly.
Thanks for the advice guys. I did some more tests tonight, and could hear lots of air flow coming through the bottom of the engine when triggering the throttle. Makes me concerned that the head gasket may be cracked… The purge solenoid is only a $30 part so I may as well replace it and see if it makes a difference. But I feel like the real issue may be the gasket… The ECT sensor is also a odd issue because my engine temps are reading normally.
It may not be the ect sensor that is giving the code. If the thermostat sticks open, or the rubber gasket around the thermostat has a breach, the car won’t come up to operating temp. This will give the code about the ect sensor (coolant temp is too low per ect sensor).
I still think your idle air control valve may be gummed up or faulty. So I’d clean the iac plunger and the throttle body. The air sucking sound reminds me of a plugged iac port or iac valve failed closed.
That’s puzzling. Have no idea what would be causing that. Check the brake power booster to insure it isn’t leaking vacuum. If the diaphragm inside that part breaks it can make a sort of hissing noise. It would have to be a very unusual sort of head gasket failure to cause that noise, but I suppose such a thing is possible. A length of old garden hose can be used as a stethoscope to narrow down where exactly a noise is coming from sometimes.
The above posts are right about solving the cooling system under-temperature problem before assuming there are any other problems besides that. Modern engines just don’t run well if they aren’t at the correct coolant temperature. As far as the poor engine performance being due to the evap system, if that were the case it would most likely either be due to the purge valve, opening when it shouldn’t, or the fuel tank is having a vacuum develop inside it as you drive. That could prevent fuel from being pumped from the tank. You might try (as a test only) seeing if the engine performance problem improves if the gas cap is loosened a little.
Common sense says the most likely causes are
-
bad gas (since the symptom occurred immediately after a fill-up. If your shop an get a sample from the tank, they could let it sit overnight then tell if it was separating into layers, indicating water in the gas.
-
egr is sticking open
-
fuel pressure is incorrect
-
unmetered air getting into the engine
The reason I placed those two at the end of the list is b/c usually either would cause an air/fuel mixture code, which you don’t seem to have. There is the chance that mixture codes are suppressed by the computer when the engine coolant temperature is too low.
PCV system problems can sometimes cause hissing noises, so checking that system makes sense.