Misfire while cruising

Tiny
CHRIS LOWDERMILK
  • MEMBER
  • 2010 SUBARU FORESTER
  • 2.5L
  • 4 CYL
  • AWD
  • AUTOMATIC
  • 81,000 MILES
I am getting a light misfire while cruising and when the engine is hot (especially on hot days). When the misfire occurs is sounds like a little poof and the is a light buck back in the gas pedal. I have changed the spark plugs and that did not fix it. Please help.
Wednesday, June 15th, 2016 AT 7:19 PM

8 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Are you setting any misfire codes for certain cylinders? Also is it worse with the air conditioner is on?
Was this
answer
helpful?
Yes
No
Wednesday, June 15th, 2016 AT 8:17 PM
Tiny
CHRIS LOWDERMILK
  • MEMBER
  • 5 POSTS
Sorry about the delayed response. I had a local mechanic my employer works with hook it up to the computer and he couldn't find anything. His suggestion was to change the plug wires and boots. I did that over the weekend and it seems to have made the problem less apparent but it's still there. It also only happens with the AC on. If I turn the AC on while driving, I will notice an initial miss as soon as it turns on. My guess is a bad ignition coil but would like another opinion before changing for around $180 (parts only).
Was this
answer
helpful?
Yes
No
Monday, June 20th, 2016 AT 7:33 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,622 POSTS
Hey Chris,

It sounds like it could be the mass air flow sensor, have you cleaned it recently? That sometimes works but if not replacement will help because cleaning only works sometimes. Here are two guides that should help you.

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

and

https://www.2carpros.com/articles/mass-air-flow-service

Let me know how ti turns out

Best, Ken

Was this
answer
helpful?
Yes
No
Monday, June 20th, 2016 AT 10:03 PM
Tiny
CHRIS LOWDERMILK
  • MEMBER
  • 5 POSTS
So I cleaned the MAF last night, but the hesitation is still there. It's almost as if when the AC compressor kicks on, there is a drop in power which is what I am feeling. However, I had a 2011 Impreza (very similar internals as the Forester) before this and didn't have any issues. I feel like there my be an issue with the electricity distribution system (fuses, relays, or alternator).
Was this
answer
helpful?
Yes
No
Wednesday, June 22nd, 2016 AT 5:51 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,622 POSTS
It could be going into limp mode, can you scan for codes to see if there is any present? Here is a guide

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Let me know

Best, Ken

Was this
answer
helpful?
Yes
No
Wednesday, June 22nd, 2016 AT 8:32 AM
Tiny
CHRIS LOWDERMILK
  • MEMBER
  • 5 POSTS
I have finally figured it out! The hesitation was caused by the AC compressor working overtime. That was caused by a low level of refrigerant. I added around 8 ounces of r134 and everything has smoothed out. I can't believe something as simple as that caused such a nuisance.
Was this
answer
helpful?
Yes
No
Sunday, June 26th, 2016 AT 9:10 AM
Tiny
CHRIS LOWDERMILK
  • MEMBER
  • 5 POSTS
Also, thank you everybody for chiming in and helping out. I'm sure it didn't hurt to clean up some other parts in the process!
Was this
answer
helpful?
Yes
No
Sunday, June 26th, 2016 AT 9:11 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,622 POSTS
Yep, it never hurts to do extra while helping your car run better. We are glad you found out the problem, it will help others. Please use 2CarPros anytime we are here to help.
Was this
answer
helpful?
Yes
No
Sunday, June 26th, 2016 AT 9:14 AM

Please login or register to post a reply.

Related Engine Misfire Content

Intermittent Misfire
VIDEO
Intermittent Misfire
In­struc­tional re­pair video
Misfire Random Code P0300
GUIDE
Misfire Random Code P0300
The world of au­to­mo­tive di­ag­nos­tics can be com­plex, with nu­mer­ous codes and po­ten­tial is­sues to keep track of. One of the more com­mon en­gine di­ag­nos­tic codes is P0300, which...
VIEW MORE