# Misfiring problem **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [July 16, 2011, 12:47am UTC](https://community.cartalk.com/t/misfiring-problem/66279 "2011-07-16T00:47:03Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 16, 2011, 12:47am UTC](https://community.cartalk.com/t/misfiring-problem/66279/1 "2011-07-16T00:47:03Z")
i got a 1997 sonoma which has a p0300 code. i changed the plugs and wires, cap and rotor and the pcv value, and it still misses. what could this be? please help. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 16, 2011, 12:56am UTC](https://community.cartalk.com/t/misfiring-problem/66279/2 "2011-07-16T00:56:57Z")
The problem might be with a dirty/defective Mass Air Flow sensor. This can cause a multiple cylinder misfire code. You might first try obtaining a can of aerosol MAF sensor cleaner and give the MAF sensor a good cleaning. If that shows no improvement then what should be done is connect a scan tool that can do real time monitoring. Take the vehicle for a drive, and then monitor the relationship of throttle position to the amount of air the MAF sensor is detecting. If at 100% open throttle the MAF sensor detects only 85% mass air flow there’s a problem with the MAF sensor. Tester ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 16, 2011, 1:00am UTC](https://community.cartalk.com/t/misfiring-problem/66279/3 "2011-07-16T01:00:45Z")
could i use an air blower on that mass air flow sensor ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 16, 2011, 1:10am UTC](https://community.cartalk.com/t/misfiring-problem/66279/4 "2011-07-16T01:10:29Z")
if it turns out not to be that mass air flow sensor, what else could cause that? ---
**Author:** ![keith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/keith/32/5518_2.png) [@keith](https://community.cartalk.com/u/keith)\ **Post date:** [July 16, 2011, 2:33am UTC](https://community.cartalk.com/t/misfiring-problem/66279/5 "2011-07-16T02:33:49Z")
“could i use an air blower on that mass air flow sensor” No that would damage it. There is a cleaner made special for it. ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 16, 2011, 3:16am UTC](https://community.cartalk.com/t/misfiring-problem/66279/6 "2011-07-16T03:16:29Z")
could a thermostat cause a misfire? ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [July 16, 2011, 10:11am UTC](https://community.cartalk.com/t/misfiring-problem/66279/7 "2011-07-16T10:11:55Z")
Cleaning the MAF sensor may very well clear the trouble. Check for any vacuum leaks passed the MAF sensor also. I don’t think the thermostat will have much influence on this trouble. A faulty cam sensor or knock sensor could also cause the trouble I think. ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 16, 2011, 1:39pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/8 "2011-07-16T13:39:09Z")
how do i clean that sensor properly ---
**Author:** ![nevadawrench](https://avatars.discourse-cdn.com/v4/letter/n/f1d935/32.png) [@nevadawrench](https://community.cartalk.com/u/nevadawrench)\ **Post date:** [July 16, 2011, 2:14pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/9 "2011-07-16T14:14:29Z")
Some auto parts stores will actually carry a specific air flow cleaner. I have successfullly used a more general “electric motor and parts cleaner” as well. ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 16, 2011, 2:18pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/10 "2011-07-16T14:18:13Z")
ok thanks but will that turn the p0300 code off ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [July 16, 2011, 3:22pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/11 "2011-07-16T15:22:25Z")
After whatever is causing the trouble is fixed it may take a number of drive cycles for the CEL light to go out. Some codes clear as soon as the trouble is fixed and some require a number of drive cycles before they go away. Clearing the codes will make it go away immediately. ---
**Author:** ![keith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/keith/32/5518_2.png) [@keith](https://community.cartalk.com/u/keith)\ **Post date:** [July 16, 2011, 4:02pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/12 "2011-07-16T16:02:40Z")
I have not seen a thermostat cause a misfire, but I don’t know that it couldn’t. I just don’t see how. The P0300 is a misfire that is random, the engine can’t figure out which cylinder is misfiring. If one cylinder had a steady misfire, then you would get a P030x with x telling you which cylinder. Have you modified the air cleaner assembly by putting on a cold air intake or use a K&N air filter? This can be the source of your P0300 and MAF sensor problems. If you did, and you want to keep it, you need to keep a can of CRC Mass Air Flow Sensor Cleaner handy. ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 16, 2011, 4:10pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/13 "2011-07-16T16:10:42Z")
no it is all factory so the possiblity would be that mass air flow sensor dirty ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 17, 2011, 11:30pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/14 "2011-07-17T23:30:01Z")
well here is what the truck is doing you drive it it runs nice and when u stop at a stop sign it runs rough and shakes ---
**Author:** ![keith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/keith/32/5518_2.png) [@keith](https://community.cartalk.com/u/keith)\ **Post date:** [July 17, 2011, 11:48pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/15 "2011-07-17T23:48:49Z")
You could have a dirty maf sensor, a vacuum leak, a burned valve, a fuel problem like a dirty filter or fuel pump issue, a stuck egr valve, or a number of other things. ---
**Author:** ![automechanic1993](https://avatars.discourse-cdn.com/v4/letter/a/a9a28c/32.png) [@automechanic1993](https://community.cartalk.com/u/automechanic1993)\ **Post date:** [July 24, 2011, 9:40pm UTC](https://community.cartalk.com/t/misfiring-problem/66279/16 "2011-07-24T21:40:51Z")
thank for the advice i will check the fuel filter first then go from there. ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [July 25, 2011, 12:49am UTC](https://community.cartalk.com/t/misfiring-problem/66279/17 "2011-07-25T00:49:04Z")
With a random misfire code I’d check the crankshaft position sensor. ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [July 25, 2011, 1:02am UTC](https://community.cartalk.com/t/misfiring-problem/66279/18 "2011-07-25T01:02:09Z")
Out of curiosity, why do you ask about the thermostat? If there is reason to suspect a problem you should deal with it. If it is stuck open the car will run too cool & that means it will continually run rich. Its isn’t outside of the realm of possibility that this could cause a misfire. In addition to cleaning the MAF & checking for vacuum / intake leaks I’d also want to put a fuel pressure gauge on it, though that is unrelated to possible concerns about the thermostat. ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [July 25, 2011, 1:09am UTC](https://community.cartalk.com/t/misfiring-problem/66279/19 "2011-07-25T01:09:03Z")
I missed the post about running fine and shaking at idle only so retract the crank sensor comment.