I have a 2001 Pontiac Grand Am SE. The last few days I have been having a weird problem with my car’s acceleration. It only happens the first time I start the car and drive it.
So I put my key in and start the car and everything sounds ok. I put it in Reverse and back out of my driveway pressing the brakes, everything still ok. I change to Drive and start pressing the gas pedal but the car has trouble accelerating. Like it barely accelerates at all. I’m not sure how to describe it but the car feels unstable, a little bit shaking/rumbling. I keep pressing the gas pedal for a few more seconds and everything is normal again. So total time from can’t accelerate at all to normal acceleration is less than 20 to 30 seconds.
If I drive somewhere like the gas station or grocery store and turn the car off then later start it again, it doesn’t happen at all. It only happens the first time starting the car. I also got a P0171 code which looks like I probably have an air or fuel problem.
I already checked all hoses and I don’t think there is a vacuum leak. Maybe fuel injectors getting clogged up and not spraying fast enough? Should I use fuel system cleaner? I changed fuel filter two years ago.
I would check the fuel pressure during a cold start it may be getting weak. If you have a scan tool check the inlet air temperature and coolant temp when cold… should be the same as ambiant temp… and again when warm. Inlet should be a bit higher than ambiant but coolant should be 180 to 200. Check short and long term fuel trims as well.
FWIW, I had a similar symptom on my much older carbureted truck, which turned out to be a fuel problem. I think @Mustangman 's idea for a shop fuel pressure check is where to start. If low fuel pressure, the fuel pump is probably on its last legs. Could be an electrical problem as well; e.g. corroded connection at fuel pump or its ground.
We don’t know if your driveway is downhill or not backing out, if downhill that might be why it backs out ok…
You also didn’t say if the engine was revving up when pressing the gas pedal and not moving or not…
You either have the 4T40E (2.4L) or 4T45E (3.4L) transaxle and neither has a dipstick, so you will have to know where the check plug is and correct way to check the fluid level or have it checked by a pro shop to see if it is low or not…
I’m sure YT has some videos out there…
Do the key dance before trying to start the car in the morning, if it starts and runs/drives normal then it is your fuel pressure bleeding off/draining back into the gas tank overnight… Only because it is a simple test to eliminate it as a possible problem…
For a long post, you didn’t give us the details we really needed…lol
This is the 4-cylinder Pontiac with excessive wheel spin when leaving a traffic light and with all the warning lights on. Someone needs to road test this vehicle and make an honest assessment of the malfunction(s).
No, just normal engine sound, no rev. No matter how hard I press the gas pedal, it struggles to accelerate. Then after a few seconds of keep pressing the gas pedal, it makes a sudden, quick acceleration and I can drive it like usual. Until I have to release the gas pedal at a red light and it starts doing the same thing again. Maybe something is clogged up?
I have been backing out of this driveway for years so it is not the problem.
I went to a car mechanic and the car was hesitating really bad on the way there. It was doing so at every red light. Even at normal speed like 45 mph, the car felt heavy and didn’t have as much power as normally would.
The car mechanic sat in the car and rev up the engine before taking a test drive. He came back and said it was driving ok. I also drove the car right after and now it is driving ok, not sure if it is just temporarily. He said maybe to use 93 gas instead.
I remember having a P0171 code around the same time and it went away after I rev up the engine while idling. Why does this happen?
Should I change the fuel filter, I think maybe it is clogged? But I changed it in early 2022.
@Mustangman suggested a fuel-trim test in the post above . Have you done that yet? It’s a relatively quick test for a shop having the necessary scan-tool equipment.
Here is the freeze frame for P0171 code:
Load Pct (%): 87.8
ETC (F): 190
Short term fuel %: 12.5
Long term fuel %: 14.1
MAP (inHg): 26.6
RPM /min: 1829
VSS (mph): 52
Live data (plugged in code reader after didn’t drive car for one day):
Load Pct (%): 100
ETC (F): 82
Short term fuel %: 0
Long term fuel %: 4.7
MAP (inHg): 29.2
RPM /min: 0
VSS (mph): 0
IAT (F): 82
TP (%): 0
O2B1S1 (V): 0.445
Short term B1S1 (%): 0
O2B1S2 (V): 0
Just started the car:
Load Pct (%): 22.4
ETC (F): 84
Short term fuel %: around 5, changing any number from 0 to 9
Long term fuel %: 8.6
MAP (inHg): 9.5
RPM /min: 1295
VSS (mph): 0
IAT (F): 82
TP (%): 1.6
O2B1S1 (V): 0.950
Short term B1S1 (%): 5.5
O2B1S2 (V): 0.710
Rev up to 2200 RPM
Load Pct (%): 32.5
ETC (F): 118
Short term fuel %: 0 to 3
Long term fuel %: 13.3
MAP (inHg): 10
RPM /min: 2253
VSS (mph): 0
IAT (F): 82
TP (%):6.7
O2B1S1 (V): 0.73
Short term B1S1 (%): -17.2
O2B1S2 (V): 0.775
There’s definitely some indications the engine is running overly lean. There’s several long term fuel trims over 10% for example. The best dataset for diagnostic purposes is the first one, the freeze frame for p0171. I presume the car was warmed up at the time. The coolant temp looks good, MAP looks a little on the high side for 1829 rpm, but might be ok given the 87% engine load. Were you accelerating or going uphill? The long term fuel trim seems to be the key diagnostic parameter, over 10% is too high. There’s too much oxygen in the exhaust stream, and this needs to be explained. Common causes: exhaust system leak, vacuum system leaks. Ask your shop to check for exhaust leaks especially where the exhaust manifold bolts to the head, and the flex tube (usually) near the exhaust manifold. Replace any broken exhaust hangers.
A display of the O2 sensor output waveform at warm idle would be helpful as well.
It is strange that I can fix the problem temporarily by revving the car before driving the car. I also got a P0171 code that went away after revving the car. I guess it somehow corrects the air and fuel ratio problem? Maybe the problem is one of these 3 sensors?
Throttle Position Sensor, Air Idle Control Valve, MAP Sensor
IIRC one of the posters above recommend to have your shop check the throttle position sensor function. Given the relationship to revving the engine, doing some testing to eliminate the throttle position sensor as the culprit makes a lot of sense imo. If you can provide a display of the O2 sensor waveform at warm idle, that would be helpful if you want more ideas here.