Q: Car hesitation from stop to acceleration

asked by on

I put a new fuel pump and filter in my SUV after the old one went bad. It then started to give me a code 35 IAC. I replaced my IAC and idle was normal and not super high anymore. No more codes. I have put a new MAP sensor, throttle body sensor, spark plugs and wires (in correct firing order), vacuum lines, distributor cap, and rotor. However, it is still hesitating hard while accelerating and has miner surges like less than 50rpm and its noticeable while driving with small jerks like its trying to catch up. Any advice? Also, the spark plug gap says it should be .035 and I bought the iridium plugs that are pre gapped at .055 as advised by the auto shop.

My car has 193352 miles.
My car has an automatic transmission.

Hi, thanks for writing in. Prior to further diagnostics you should install the spark plugs that are referred to in the factory service manual and/or obtain the plugs from a GM dealer. Installing alternative aftermarket plugs with different gaps, materials, heat ranges, and what have is OK if you are set up as laboratory to do testing but if not you have to go with OEM on plugs. GM has already agonized over the correct plugs for the vehicle and has spent millions of dollars on testing. Benefit from their experience. If an auto parts store tells you to use a part that is materially different that which is clearly documented in the Factory Service manual, 10 times out of ten the store is wrong and the Manual is right.

Given the age of the vehicle, I would consider the fuel injectors (remove and send to a lab for cleaning, for example Mr. Injector), vacuum leaks, and ignition wiring issues as a cause of the hesitation. But before checking those, install the plugs recommended by GM for the vehicle because that is the only way to eliminate a misspecification there as even a part cause of the hesitation. On a 20 plus year old vehicle, I would have the injectors professionally cleaned and tested no matter what symptoms you are having, but particularly if it is hesitation.

If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Car hesitation from stop to acceleration

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

Get a quote

What others are asking

Q: Q: Timing off

The pinion teeth of the starter motor engage with the teeth on the flex plate, and the starter motor cranks over the engine. I don't see how you could have messed up your timing during a starter replacement. But it...

Q: Speedometer and Odometer stopped working.

The speedometer on your Mustang is electronically controlled. The speedometer is powered on the light green with yellow stripe wire from the #8 fuse in the dash panel fuse box. The grey/black and the green/orange wires go to the vehicle...

Q: Rocker Arms

Hi Ricky. Thanks for contacting us today. Today's modern engines don't have older style; individual rocker arms. They are in an assembly (or multiple ones) that are replaced as a set if one is damaged. Intake rocker arm assemblies are...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...