Need solution for hunting idle
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Need solution for hunting idle
1989. Auto. 52000 miles
runs great except at idle. At idle the engine was to hunt up and down Not too bad, but enough to idle on the rough side. I tuned idle up to 750 so it’s not as bad at 650 rpm. I think it has stock cam, but not sure. I have tested, fixed, or replaced everything from ecu to maf. The only thing I have not replaced is the distributor itself, and I even have a spare one of those. I have checked for vacuum leaks with smoke, propane and other ways and can find no leakks. I have even plugged off everything not needed to make engine run, but nothing has worked I have beee working on this problem for going on 5 years. The car had 47000 when I bought it
I am somewhat convinced the problem might be in the tune. I have tunerpro rt and an ostrich. I have made some changes but it was things like fan on and off, idle rpm at idle and so forth. Nothing to do with spark, air or fuel
im looking for some advise on a simple way to make changes to tune at idle only, or at least what to try, like trying to make it richer or leaner at idle
i have done all normal adjustments and I even have MT2500 scanner and computer to check settings. This problem is getting very old and has been very expensive and time consuming
Mike
runs great except at idle. At idle the engine was to hunt up and down Not too bad, but enough to idle on the rough side. I tuned idle up to 750 so it’s not as bad at 650 rpm. I think it has stock cam, but not sure. I have tested, fixed, or replaced everything from ecu to maf. The only thing I have not replaced is the distributor itself, and I even have a spare one of those. I have checked for vacuum leaks with smoke, propane and other ways and can find no leakks. I have even plugged off everything not needed to make engine run, but nothing has worked I have beee working on this problem for going on 5 years. The car had 47000 when I bought it
I am somewhat convinced the problem might be in the tune. I have tunerpro rt and an ostrich. I have made some changes but it was things like fan on and off, idle rpm at idle and so forth. Nothing to do with spark, air or fuel
im looking for some advise on a simple way to make changes to tune at idle only, or at least what to try, like trying to make it richer or leaner at idle
i have done all normal adjustments and I even have MT2500 scanner and computer to check settings. This problem is getting very old and has been very expensive and time consuming
Mike
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Have you cleaned the passage way under the throttle body and or replaced the IAC? These have major impact on idle. Another thing that will mess with the idle is injectors. Check to see if they are firing with NOID lights. You might have a bad injector electrical plug.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Do you still have stock chip? TPS setting , IAC counts, iNT/ BLN? If you can put stock chip in and car straightened out it's your tune. Is IAC hunting causing idle issue.
A worn distributor could cause it. Timing would be changing while in set timing mode. You might notice some wobble in rotor, a worn cam gear another possibility.
MAF sensor or air leak between sensor and throttle body.
egr valve trying to open at idle.
A worn distributor could cause it. Timing would be changing while in set timing mode. You might notice some wobble in rotor, a worn cam gear another possibility.
MAF sensor or air leak between sensor and throttle body.
egr valve trying to open at idle.
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
Have you done a basic idle adjustment in order, cures mine every time.
http://www.digitalcorvettes.com/foru...ad.php?t=58873
Also make sure no codes for lean bank(O2 sensors)
http://www.digitalcorvettes.com/foru...ad.php?t=58873
Also make sure no codes for lean bank(O2 sensors)
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
Check the vacuum, then refer to a trouble table (not handy) for guidance. In this e-age, the old tools still have great value and this is free and simple!
I suspect the ECM is trying to adjust for input outside its norm, such as unmetered air entry, causing a lean burn. 'Reading' plugs may also help, but is more work.
Old Motor manuals oft have charts for both the above.
I suspect the ECM is trying to adjust for input outside its norm, such as unmetered air entry, causing a lean burn. 'Reading' plugs may also help, but is more work.
Old Motor manuals oft have charts for both the above.
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Have done all those things mentioned many times. Plugs look good, and I have changed brand, gaps many times. No vacuum leaks. As I have stated I have done almost everything one can think of. I have only two things I can think of mechanically. Distributor or loose timing chain. I have extra distributor
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Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
No egr or air pump Stock chip makes no difference. New maf and no air leaks. I have another distributor I will try
INT and BLN are in the acceptable range
INT and BLN are in the acceptable range
Do you still have stock chip? TPS setting , IAC counts, iNT/ BLN? If you can put stock chip in and car straightened out it's your tune. Is IAC hunting causing idle issue.
A worn distributor could cause it. Timing would be changing while in set timing mode. You might notice some wobble in rotor, a worn cam gear another possibility.
MAF sensor or air leak between sensor and throttle body.
egr valve trying to open at idle.
A worn distributor could cause it. Timing would be changing while in set timing mode. You might notice some wobble in rotor, a worn cam gear another possibility.
MAF sensor or air leak between sensor and throttle body.
egr valve trying to open at idle.
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Done many times
no codes
no codes
Have you done a basic idle adjustment in order, cures mine every time.
http://www.digitalcorvettes.com/foru...ad.php?t=58873
Also make sure no codes for lean bank(O2 sensors)
http://www.digitalcorvettes.com/foru...ad.php?t=58873
Also make sure no codes for lean bank(O2 sensors)
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Power balance ? Injector balance? Does O2 read from > .9 - .1< ? Cross counts? Was egr valve disabled or removed? MAP reading at idle? You could measure valve lift as a way to check if cam is stock. It's unlikely aftermarket cam will have stock lift.
Last edited by Kevova; Nov 28, 2017 at 11:59 AM.
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Really appreciate everyone trying to help. No idea is too small to try
no vacuum leaks I removed egr because I thought that might have been problem. Injectors are fairly new. I replaced them because car had originals. I even sent them off to FIC. To be rebuild. Don’t know about cam, if it’s original or not. I have computer and mt2500, but not sure about measuring maf.
no vacuum leaks I removed egr because I thought that might have been problem. Injectors are fairly new. I replaced them because car had originals. I even sent them off to FIC. To be rebuild. Don’t know about cam, if it’s original or not. I have computer and mt2500, but not sure about measuring maf.
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
There's more to vacuum diagnosis than the number, including unsteadiness, fast or slow, in the needle. It can indicate late timing, valve issues and a lot more.
One reference from my non-G**gle search: http://www.onallcylinders.com/2015/0...gine-problems/
One reference from my non-G**gle search: http://www.onallcylinders.com/2015/0...gine-problems/
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Good idea. I replaced head gaskets and did not see grounds at the back of heads when I took them off. Instead of checking ALL grounds, I was thinking of running a new ground wire, but not sure to connect it to
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
anyone know where the ecu ground point is on 89 with auto trans?
