High fuel consumption, 12.1 mpg on vehicle computer in city, hesitation on acceleration.


Asked by Oct 23, 2016 at 12:33 AM about the 2002 Pontiac Grand Prix GT

Question type: Maintenance & Repair

No service of check engine lights. 130,000 miles, recent spark plugs and
cables changed, both manifold and valve cover gaskets replaced, new
transmission, changed fuel filter about 5000 miles ago. However, I did put 4
bottles of fuel injector cleaner over the course of about 6 fill ups. I have not
had throttle body serviced, or mass air flow sensor checked.? I am
concerned if all the fuel injector cleaner may have damaged fuel filter, or
loosened tank deposits, that may have restricted fuel filter. I believe air filter
was checked not too long ago. Also, I began noticing, than if I take off from
a cold start, sometimes it tends to hesitate a little, but only until it warms up.  
I keep my car maintained, and for the 5 years I have owned it, never has it
let me down, or stranded. A little help please.???

8 Answers


Changing the fuel filter is no bid deal so you may want to go ahead with that but it would not cause a huge drop in gas mileage. Check for fuel leaks. Do an actual mileage test by filling the car up, writing down the mileage and then again at the next fill up. Calculate the mileage after a couple of hundred miles to make sure the computer is not off for some reason.

1 out of 1 people think this is helpful.

Thanks for the response, but I failed to mention that fuel consumption has been a problem for a few years now, and nothing I have done seems to help. I will check for fuel leaks, but what about the hesitation, this is something new, and it has never hesitated. That is why i was concerned about mass air flow sensor being dirty, or the throttle body. ???


Maybe your fuel injectors are leaking or the mass air sensor is off. I would have a mechanic check to see if your emissions show that the car is running really rich. What did the spark plugs look like when you changed them? Sooty?

1 out of 1 people think this is helpful.

Sounds like you've lost overdrive and torque converter clutch (TCC) lock in. Very common with these cars. At cruising speed (55 or so MPH) your tach should be around 1500 RPMs. My '00 GT, with 155,000 miles on it has lost overdrive and TCC lock in. At 55-60 MPH the tach is at 2700 to 2900 RPMs. This kills your gas mileage. To be sure of your mileage figure it out yourself. Don't rely on the car's computer. They're not always 100% accurate. HTH. -Jim

1 out of 1 people think this is helpful.

I just had transmission rebuilt, because I had lost overdrive, was doing 3000 rpms at 60 mph. Now, 15-1600 rpms. TTC was defective until 2003 when manf. corrected. The spark plugs still looked good, like they did not need to be changed. It has always passed smog on first test. I am going to clean the mass air flow sensor, that I have not done. Thanks.

1 out of 1 people think this is helpful.

You're welcome. Glad to help. -Jim


What trouble codes came up when you had it scanned?


Have not had it scanned. Drove a 150 miles yesterday on freeway, hesitation on acceleration, almost seems like it is starving for air or fuel. Okay once I get to the desired speed. I averaged about 20 mpg. Thanks.

Your Answer

Add photo

Related Questions

  • Hesitation when accelerating 5 answers

    I have 01 Pontiac Grand Prix, the last couple weeks it's been hesitating when accelerating. Spark plugs and wires just replaced, new fuel filter replaced and injectors cleaned too. I took it in tod...

    2001 Pontiac Grand Prix


    Maintenance & Repair

  • Hard acceleration 2 answers

    I have a 2004 Grand Prix with about 150,000 miles on it!! Just recently it became hard for me to accerlate! And sometimes before taking off or when I come to a stop n press the accelerate it hesita...

    2004 Pontiac Grand Prix GT1


    Maintenance & Repair

  • 04 GTP Comp G Hesitates 1 answer

    Hesitates from starting on a incline, or at hard acceleration. Replaced Cat Converter, Fuel filter, plugs, no error lights, at a loss. Coil packs???

    2004 Pontiac Grand Prix GTP


    Maintenance & Repair

  • acceleration problems 8 answers

    car is services every 2000 mi/now has 115000 mi/just had first tune up, which did not fix the problem. It started about 3 wks ago when I accelerate the gas, at any speed, it wants to hesitate..like...

    2006 Pontiac Grand Prix Base


    Maintenance & Repair

  • There is a hesitation/lag when first pushing on the accelerator. Is this common and can it be fixed at the dealer? 13 answers

    2007 Pontiac G6 GT Convertible


    Maintenance & Repair

Grand Prix

Looking for a Used Grand Prix in your area?

CarGurus has 2,919 nationwide Grand Prix listings starting at $1,995.


Search Pontiac Grand Prix Questions

Pontiac Grand Prix Experts

#1 Js08016
Reputation 4,120
#2 Tom Demyan
Tom Demyan
Reputation 2,780
#3 munron
Reputation 2,150
View All

Related Models For Sale

Used Chevrolet Impala
523 Great Deals out of 29,877 listings starting at $799
Used Pontiac Bonneville
542 listings starting at $3,699
Used Chevrolet Monte Carlo
17 Great Deals out of 1,380 listings starting at $1,995
Used Pontiac Grand Am
1,254 listings starting at $1,593
Used Ford Mustang
388 Great Deals out of 47,511 listings starting at $1,800
Used Chevrolet Malibu
864 Great Deals out of 81,222 listings starting at $995
Used Chevrolet Camaro
148 Great Deals out of 32,614 listings starting at $1,729
Used Pontiac Firebird
6 Great Deals out of 745 listings starting at $2,500
Used Honda Accord
769 Great Deals out of 88,117 listings starting at $1,150

Used Cars For Sale

2007 Pontiac Grand Prix GT For Sale
77 listings starting at $2,999