Engine RPM's jumping around at idle and driving
12-24-2011, 12:43 PM
#1
Junior Member
Thread Starter
Join Date: Jul 2011
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
Engine RPM's jumping around at idle and driving
Hey guys recently my 88 Firebird Formula with a 350 and auto trans has been running a little rough at idle the rpm's are very jumpy going from 500 rpm s and spiking randomly to about 700 rpms more noticeably is driving on the highway. Doing about 65 at 2k leveling out the gas pedal my rps are going from 2000 spiking/jumping to 2500/2700 and you can feel it the whole ride.
Recently i changed my MAF sensor because it was bad i also changed my transmission mount because it needed to be swaped.
i dont think its a transmission issue because when i put the car in neutral the rpms are still rough could this be a misfire? the previous owner changed the sparkplug wires less than 10k miles ago. any ideas guys?
Recently i changed my MAF sensor because it was bad i also changed my transmission mount because it needed to be swaped.
i dont think its a transmission issue because when i put the car in neutral the rpms are still rough could this be a misfire? the previous owner changed the sparkplug wires less than 10k miles ago. any ideas guys?
Last edited by xsvtank; 12-24-2011 at 08:14 PM.
12-24-2011, 08:36 PM
#4
Re: Engine RPM's jumping around at idle and driving
You need to check the throttle postion sensor, use a volt meter or a scanner, it should be in the voltage spec & increase in voltage smoothly.
Get a fuel pressure tester, tape it to the windshield & drive it, note the pressure.
Test the coolant temp sensor, this has a big impact on idle speed. You can test it w/ a scanner or remove it & test it w/ an ohm meter in a pan of water. The resistence changes alot from cold to 200*. You'll need a thermometer too. You can find the ohm values on the web.
Check your grounds esp. the ecm grounds, usually at the back of the heads or near the t stat housing.
Make sure the distributor is in good shape, sometimes they will get loose from high mileage & cause weird problems.
I don't know if your maf sensor has a relay, check to see if the maf is getting the proper voltage.
Get a fuel pressure tester, tape it to the windshield & drive it, note the pressure.
Test the coolant temp sensor, this has a big impact on idle speed. You can test it w/ a scanner or remove it & test it w/ an ohm meter in a pan of water. The resistence changes alot from cold to 200*. You'll need a thermometer too. You can find the ohm values on the web.
Check your grounds esp. the ecm grounds, usually at the back of the heads or near the t stat housing.
Make sure the distributor is in good shape, sometimes they will get loose from high mileage & cause weird problems.
I don't know if your maf sensor has a relay, check to see if the maf is getting the proper voltage.
12-25-2011, 12:14 AM
#5
Junior Member
Thread Starter
Join Date: Jul 2011
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
Re: Engine RPM's jumping around at idle and driving
You need to check the throttle postion sensor, use a volt meter or a scanner, it should be in the voltage spec & increase in voltage smoothly.
Get a fuel pressure tester, tape it to the windshield & drive it, note the pressure.
Test the coolant temp sensor, this has a big impact on idle speed. You can test it w/ a scanner or remove it & test it w/ an ohm meter in a pan of water. The resistence changes alot from cold to 200*. You'll need a thermometer too. You can find the ohm values on the web.
Check your grounds esp. the ecm grounds, usually at the back of the heads or near the t stat housing.
Make sure the distributor is in good shape, sometimes they will get loose from high mileage & cause weird problems.
I don't know if your maf sensor has a relay, check to see if the maf is getting the proper voltage.
Get a fuel pressure tester, tape it to the windshield & drive it, note the pressure.
Test the coolant temp sensor, this has a big impact on idle speed. You can test it w/ a scanner or remove it & test it w/ an ohm meter in a pan of water. The resistence changes alot from cold to 200*. You'll need a thermometer too. You can find the ohm values on the web.
Check your grounds esp. the ecm grounds, usually at the back of the heads or near the t stat housing.
Make sure the distributor is in good shape, sometimes they will get loose from high mileage & cause weird problems.
I don't know if your maf sensor has a relay, check to see if the maf is getting the proper voltage.
12-26-2011, 11:10 AM
#6
Junior Member
Join Date: Dec 2011
Location: Newfoundland
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
Car: 84 Trans Am
Engine: 305 for now
Transmission: 5spd
Re: Engine RPM's jumping around at idle and driving
Also check for a vacuum leak, your rpms serging at idle and while driving can sometimes indicate a vacuum leak,
Thread
Thread Starter
Forum
Replies
Last Post
db057
TBI
10
08-11-2015 10:11 PM
