85 vette
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Hi.
I have an 85 as well. What disturbs me a little is that you say it happens once in a while. Bad idle can have a lot of reasons.
The number one is carbon deposits in the throttlebody behind the butterfly valve in the main opening.Then in the IAC valve system. Take out the Idle Air Control valve which can be screwed out and clean the pintle and valveseat and also the openings. If this does not help then
Search for vacuum leakages. This you can do by checking the vacuu, lines Those underneith the plenum is very brittle after 21 years and may have broken. Then the rubbe ones must also bechecked.. Then spray startgas or propane over the runners at the plenum and also over the intake part and check if the engine changes the rpms. If so there is a leak and it must be fixed.
Check the PCV valve at the valvecover for proper operation you should hear the bullet inside rattleing if shaken.
If these are not working check the EGR sytem for proper operation and here the EGR valve is essential. It is placed under the plenum and if you apply vacuum at the vacuum intake with a vacuum pump check if the valve is moving by the help of a mirror. If it does check how long the vacuum is held . It shall hold the vacuum for at least 20 secs. So if this is not tru change the valve. Check the EGR soleoid at the passenger side for proper operation . This is described in the Heins book or workshop manual.
I had a combination of vacuum leak and EGR failure.
Then do the min. idle air adjustment as described in the workshop manual.
Good luck
I have an 85 as well. What disturbs me a little is that you say it happens once in a while. Bad idle can have a lot of reasons.
The number one is carbon deposits in the throttlebody behind the butterfly valve in the main opening.Then in the IAC valve system. Take out the Idle Air Control valve which can be screwed out and clean the pintle and valveseat and also the openings. If this does not help then
Search for vacuum leakages. This you can do by checking the vacuu, lines Those underneith the plenum is very brittle after 21 years and may have broken. Then the rubbe ones must also bechecked.. Then spray startgas or propane over the runners at the plenum and also over the intake part and check if the engine changes the rpms. If so there is a leak and it must be fixed.
Check the PCV valve at the valvecover for proper operation you should hear the bullet inside rattleing if shaken.
If these are not working check the EGR sytem for proper operation and here the EGR valve is essential. It is placed under the plenum and if you apply vacuum at the vacuum intake with a vacuum pump check if the valve is moving by the help of a mirror. If it does check how long the vacuum is held . It shall hold the vacuum for at least 20 secs. So if this is not tru change the valve. Check the EGR soleoid at the passenger side for proper operation . This is described in the Heins book or workshop manual.
I had a combination of vacuum leak and EGR failure.
Then do the min. idle air adjustment as described in the workshop manual.
Good luck
Pro
Joined: Aug 2000
Posts: 666
Likes: 0
From: Richmond TX
Originally Posted by dallasknight
me vette has started idling real bad then cuts off does not happen all the time but it does happen every once in a while any clues? most of the time it adiles perfect
Cheers,
Michael
