Idle and Emissions issues...90 model
Thread Starter
Instructor
Joined: Mar 2006
Posts: 127
Likes: 0
From: Stockbridge GA
Idle and Emissions issues...90 model
Hey guys. My baby failed emissions. The Nox was way too high. To date I have changed the EGR, Fuel pressure regulator, map sensor, injectors, O2, distributor. I think I have hit everything. Can you think of anything else that might impact the NOX reading?
Also, when I crank the car she will stall immediately. After warm up she will bobble at idle. Basically it will not hold a steady idle but fluctuate between 500-750 rpms. And she will stall every once in a while. If I hold my foot on the accellerator a little she does fine. Idle air motor? I checked for vac leaks by spraying the whole intake with starter fluid and got no fluctations in rpms.
Any suggestions are welcome.
Thanks guys!
Also, when I crank the car she will stall immediately. After warm up she will bobble at idle. Basically it will not hold a steady idle but fluctuate between 500-750 rpms. And she will stall every once in a while. If I hold my foot on the accellerator a little she does fine. Idle air motor? I checked for vac leaks by spraying the whole intake with starter fluid and got no fluctations in rpms.
Any suggestions are welcome.
Thanks guys!
Pro
Joined: Feb 2009
Posts: 541
Likes: 60
From: Auburndale Florida 1990 Vert, 6 speed
Also, when I crank the car she will stall immediately. After warm up she will bobble at idle. Basically it will not hold a steady idle but fluctuate between 500-750 rpms. And she will stall every once in a while. If I hold my foot on the accellerator a little she does fine. Idle air motor? I checked for vac leaks by spraying the whole intake with starter fluid and got no fluctations in rpms.
Any suggestions are welcome.
Thanks guys!
Any suggestions are welcome.
Thanks guys!
Thread Starter
Instructor
Joined: Mar 2006
Posts: 127
Likes: 0
From: Stockbridge GA
Le Mans Master
Joined: Jan 2008
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From: Edmonton, Alberta
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Instructor
Joined: Feb 2008
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From: Toronto Ontario
The Egr is off at idle so blocked passages are not an idle issue. If the EGR is held open at idle by carbon deposits on the EGR seat it can cause idle problems. This is just one possible causes of your problem. Before going any further get the car scanned and compare the values to factory specs. This will really help isolate the problem and prevent replacing good parts
Burning Brakes
Joined: Oct 2005
Posts: 824
Likes: 30
From: San Pablo California
The Egr is off at idle so blocked passages are not an idle issue. If the EGR is held open at idle by carbon deposits on the EGR seat it can cause idle problems. This is just one possible causes of your problem. Before going any further get the car scanned and compare the values to factory specs. This will really help isolate the problem and prevent replacing good parts
Pro
Joined: Feb 2009
Posts: 541
Likes: 60
From: Auburndale Florida 1990 Vert, 6 speed
Your TPS is non adjustable, the ECM will recalibrate it's TPS idle voltage, next time you start it up.
Engine at operating temp
Jump terminals "A" and "B" on the ALDL connector
Turn on ignition and wait 30 seconds
Unplug IAC connector
Unplug EST connector
Remove jumper and start engine
Turn off engine
Re-connect IAC and EST
Remove ECM power wire or disconnect neg terminal on battery, for 30 seconds.
Done
Engine at operating temp
Jump terminals "A" and "B" on the ALDL connector
Turn on ignition and wait 30 seconds
Unplug IAC connector
Unplug EST connector
Remove jumper and start engine
Turn off engine
Re-connect IAC and EST
Remove ECM power wire or disconnect neg terminal on battery, for 30 seconds.
Done
Corvette Enthusiast
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From: So. Cal.
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Hey guys. My baby failed emissions. The Nox was way too high. To date I have changed the EGR, Fuel pressure regulator, map sensor, injectors, O2, distributor. I think I have hit everything. Can you think of anything else that might impact the NOX reading?
Also, when I crank the car she will stall immediately. After warm up she will bobble at idle. Basically it will not hold a steady idle but fluctuate between 500-750 rpms. And she will stall every once in a while. If I hold my foot on the accellerator a little she does fine. Idle air motor? I checked for vac leaks by spraying the whole intake with starter fluid and got no fluctations in rpms.
Any suggestions are welcome.
Thanks guys!
Also, when I crank the car she will stall immediately. After warm up she will bobble at idle. Basically it will not hold a steady idle but fluctuate between 500-750 rpms. And she will stall every once in a while. If I hold my foot on the accellerator a little she does fine. Idle air motor? I checked for vac leaks by spraying the whole intake with starter fluid and got no fluctations in rpms.
Any suggestions are welcome.
Thanks guys!
Corvette Mike
Burning Brakes
Joined: Jun 2008
Posts: 892
Likes: 1
From: New Smyrna Beach Florida
What did you install for injectors? I hope you didn't puy the Multecs back in. I hope you talked to Jon at FICNJECTORS. 
Last edited by Jimbo 89; Dec 8, 2009 at 10:22 AM. Reason: spelling error
Safety Car
Joined: Jan 2004
Posts: 3,783
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From: Northern California
If you modified the exhaust flow before the catalytic converter in any way, the loss of back pressure will cause the EGR valve to not open.
Also, what is the fuel pressure? Sounds like the engine needs a complete tune up including new plugs, wires, cap & rotor at the very minimum.
Also, what is the fuel pressure? Sounds like the engine needs a complete tune up including new plugs, wires, cap & rotor at the very minimum.
Last edited by GKK; Dec 8, 2009 at 10:51 AM.
Thread Starter
Instructor
Joined: Mar 2006
Posts: 127
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From: Stockbridge GA
Car had a complete tune up less than 3K miles including new distributor, cap, rotor, coil, and wires.
I have picked up a new IAC and will get it on the car Wednesday night. I will also flush out the EGR passages at the same time. What a way to spend an evening!!
Thanks guys. I will let you know how this works out.
I have picked up a new IAC and will get it on the car Wednesday night. I will also flush out the EGR passages at the same time. What a way to spend an evening!!
Thanks guys. I will let you know how this works out.
Instructor
Joined: Oct 2007
Posts: 151
Likes: 1
Did you check the EGR solenoid valve. You can find it by tracing the EGR hose from the EGR vaslve to the Solenoid valve. Your EGr could be fine however, The EGR will not activate unless it gets the vacuum signal from the solenoid valve.
It's kind of tricky to check. I check mine by teeing into the vacuum line between the EGR and the solenoid valve. From the tee, i run a line to a vacuum gauge. The hose should be long enough that you can close your hood. then you drive along the freeway and watch the vacuum gauge. It should show system vacuum off and on as you drive. the reason you need to do this is, The EGR does not activate at idle or when in park. Goos luck
It's kind of tricky to check. I check mine by teeing into the vacuum line between the EGR and the solenoid valve. From the tee, i run a line to a vacuum gauge. The hose should be long enough that you can close your hood. then you drive along the freeway and watch the vacuum gauge. It should show system vacuum off and on as you drive. the reason you need to do this is, The EGR does not activate at idle or when in park. Goos luck
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Surprised they tested it with a surging idle.
Even with EGR, it needs a functioning CAT. You should scan it to check fuel delivery, though assuming the other test numbers (post them) were in line, it's probably close enough and if the EGR is functioning, it probably needs a new CAT. How many miles? Were any of the injectors leaking down prior to replacement? A rich condition burns up the CAT. Did the Tester offer any suggestions?
Usually, if the EGR were stuck open, it would stumble and stall - not surge.
If EGR failed to occur when commanded, it would store a troublecode and the Check Engine Light would come on until EGR was no longer needed. Again, a scan would tell you whether or not EGR was commanded and fuel delivery should swing rich if the event takes place.
Scanning data would also help you diagnose the surge. Check the MAP signal which is used for Load - Targeted Idle vs. Actual when it surges.
Even with EGR, it needs a functioning CAT. You should scan it to check fuel delivery, though assuming the other test numbers (post them) were in line, it's probably close enough and if the EGR is functioning, it probably needs a new CAT. How many miles? Were any of the injectors leaking down prior to replacement? A rich condition burns up the CAT. Did the Tester offer any suggestions?
Usually, if the EGR were stuck open, it would stumble and stall - not surge.
If EGR failed to occur when commanded, it would store a troublecode and the Check Engine Light would come on until EGR was no longer needed. Again, a scan would tell you whether or not EGR was commanded and fuel delivery should swing rich if the event takes place.
Scanning data would also help you diagnose the surge. Check the MAP signal which is used for Load - Targeted Idle vs. Actual when it surges.
Thread Starter
Instructor
Joined: Mar 2006
Posts: 127
Likes: 0
From: Stockbridge GA
The Check Engine light has come on and off since I bought the car almost 4 years ago. And the car has been running rich. I changed the IAC last night and flushed out the EGR passages. I am going to change my plugs tonight to make sure there are no carbon fouled plugs. I will let you guys know if the car passes this weekend.
Pro
Joined: Feb 2009
Posts: 541
Likes: 60
From: Auburndale Florida 1990 Vert, 6 speed
The Check Engine light has come on and off since I bought the car almost 4 years ago. And the car has been running rich. I changed the IAC last night and flushed out the EGR passages. I am going to change my plugs tonight to make sure there are no carbon fouled plugs. I will let you guys know if the car passes this weekend.