Q: Misfire at hard thottle, rpms either dont go up when accelerating, or slowly drop as i accelerate

asked by on October 25, 2016

My grand prix has began to hesitate and misfire under hard throttle, im unsure as to why which is why im asking here. This is whats been fixed and whats new on the car:

  1. Mass Airflow Sensor
  2. Manifold Absolute Pressure Sensor
  3. Spark Plugs- NGK TR6
  4. Spark Plug Wires- MSD Street Fire 8mm
  5. Ignition Coils- all 3 of them
  6. Vacuum lines running to map sensor and supercharger bypass solenoid
  7. Supercharger Bypass Solenoid
  8. Supercharger Bypass Valve
  9. Accelerator Pedal Sensor
  10. Fuel Pump- Airtex E3700M

After all this it still acted strange so I removed the fuel injectors and manually cleaned them aswell, and reinstalled with new o rings. Im at a loss as to what it is. It ran great for a long time, and I miss being able to run it like I used to. I am thinking maybe a camshaft position sensor but theres no codes to reflect that. "on a side note, I checked tps with a scan tool, its ok, but the fuel trims are a bit erratic. Thank you for your help

My car has 187000 miles.
My car has an automatic transmission.

Engine is misfiring Inspection $79.99 - $89.99 Get a Quote

Hi - check your vehicle’s fuel pressure when running, and under load. Your comment regarding "fuel trims ...erratic" gets my attention. If the pressure is not correct, check the fuel pump relay (possible burned contacts) and fuel pressure regulator. If the pressure is correct, I would suspect the injectors need professional cleaning and testing - given your mileage. I would recommend having an Engine is Misfiring Inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

What others are asking

Engine’s knocking and burning oil

In order for you to get your engine replaced as smoothly as possible, have it done by a qualified mechanic. The Ford dealer would be a good option if your vehicle is under warranty because the repair would likely be...

Having problems accelerating at high speeds causing jerking feeling...this happens when slightly pushing gas pedal

This problem of a slight jerk feel is what is known as a lean tip in surge. The cause can be an indication that the engine is running lean and may be caused by dirty injectors, throttle body, air filter,...

car shut off no water or oil in car now won't start

There are multiple reasons why your Dodge Durango may have stopped running. The water in the oil is typically a problem with a blown head gasket, but most of the time a car will stop running completely when there is...

Shuddering and hesitation on a 2015 Chevy Equinox

You'd want to pray that there was a little water in the gas and it made it do that. It's such a new vehicle. If it ever happens again, definitely take it in under warranty to see what they say...

Steaming of the engine

Hi, thanks for writing in. Codes P0107 and P0122 could show up for several reasons, such as a faulty mass air flow sensor. If you would like help, consider having an expert automotive technician from YourMechanic come to your home...

Driving on torn CV boot?

If you have been driving on torn CV boots and now have noise when turning and have driven like that for a while then you should have the axles replaced as soon as possible. You do not have to go...

Engine whines during acceleration

I believe that the noises you are hearing are indeed related to the power steering pump. If the fluid you are seeing is black, it may have metal shavings in it. These metal shavings could be a result of the...

Power steering

This suggests your power steering pump may be failing or you have a leak elsewhere in one of the power steering lines. The [power steering]((https://www.yourmechanic.com/services/power-steering-fluid-is-leaking-inspection) system operates on very high pressurized hydraulic pressure (in some cases as much as 300...

Engine shakes when I turn on the car for the first time in the day

This is somewhat normal for this car upon start up unless it is excessive. As to the check engine light, I would suggest not clearing the codes, but rather having the computer scanned by a qualified mechanic from Your Mechanic...

Related articles

How Can Problems with the Ignition System Cause Misfiring?
Misfires Misfires are never good, and they're always a sign that there’s a problem with the engine that needs to be repaired. The problem won’t “go away on its own” and waiting too long can cause the situation to grow...
How to Troubleshoot a Hesitating or Bucking Car
Hesitating cars and bucking cars often have worn out fuel filters, fuel pumps, oxygen sensors, EGR valves, spark plugs, or air filters.
How to Buy a Classic Pontiac
Whether you want to buy a classic Pontiac for yourself or as a gift, here are some tips on buying one for a great value.