Idle fluctuation
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Idle fluctuation - 8/18/2008 4:59:40 PM
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Scany
Posts: 40
Joined: 9/27/2007
Status: offline
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A little history on the vehicle:
- Engine broke due to bad bearings, new Jasper engine installed by myself
- New waterpump
- New radiator
- New distributor and cap
- New sparkplugs (wires were pretty new from the old engine)
- New flexplate
- New balancer
- The intake with fuel injectors were left untouched while the engine swap was done (about 6 months)
- Replaced the K&N cold air intake with a new one
- Transmission had slip before and after, but only at high speed and in Overdrive.
- Idle Control Valve has been replaced
- Throttle body cleaned
- Fuel filter replaced
- Measured good fuel pressure at the schraeder valve on the supply line while idling
- While installing the distributor I messed up and had to redo it all over without marks. After it started it idled and started driving a little rough. I then turned (I know the timing is automatic, but I thought I was far off) the distributor more squarely with the wires going more 90deg. out to the side of the engine. It now idles better and doesn''t stumble on initial starts.
Situation:
Especially when running the AC and putting the car in Drive, the rpms will start fluctuating at a standstill. Sometimes it''s barely noticable, and sometimes it''s pretty rough, like if I''m not firmly on the brakepedal it will lurch forward a few inches. The situation is still there when the AC is off, but it needs to be in Drive. In Neutral it''s fine and idles great. Also under power it doesn''t seem to lack any, especially from 3k rpms and up. As you see above I''ve done a few things trying to find the problem, without luck. I''m now suspecting I might have a bad fuel pump, injector(s) or torque converter. I have not yet measured fuel pressure whil the situation is present. And the situation was not there with the old engine, sort of ruling out the torque converter. Unless I broke it or somehow installed it wrong with the new engine. I fear that the fuel injectors might have dried up during the engine swap that took quite some time. My books (Dr. Whaba) told me to leave the injectors alone, as they were very fragile, but they also didn''t incorporate a 6 month repair I guess. Then again, would I not see problems while driving if the injectors are bad?
Any input on the subject would be greatly appreciated! 
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RE: Idle fluctuation - 8/18/2008 8:17:53 PM
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Scany
Posts: 40
Joined: 9/27/2007
Status: offline
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Sorry!  It''s a 99 Chevy Tahoe 5.7l Vortec 4WD.
I thought vacum could be it too, and that''s why I replaced the air intake. I guess I should go over a double check vacum. Could it be under torqued valve covers maybe? I can''t quite remember all the spots where there might be a vacum leak.
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RE: Idle fluctuation - 8/19/2008 5:51:45 PM
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jkgray80
Posts: 118
Joined: 3/20/2008
Status: offline
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You need a scan tool to set timing. Have it checked before spending any more time chasing things. Also, be sure & remove that pretty gray paint ANYWHERE a ground is.
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RE: Idle fluctuation - 8/21/2008 6:56:46 AM
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Scany
Posts: 40
Joined: 9/27/2007
Status: offline
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I had it at Chevy and told them to check/scan the timing. They just said that it didn''t show any codes so it was ok.
I will check the painted surfaces, but most of them have studs where the ground is connected. I guess there is still paint in the hole where the studs screw in. Any suggestions how to clear that out? It''ll be a pain no matter what since it''s hard to get to these places.
quote:
ORIGINAL: jkgray80
You need a scan tool to set timing. Have it checked before spending any more time chasing things. Also, be sure & remove that pretty gray paint ANYWHERE a ground is.
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RE: Idle fluctuation - 8/21/2008 7:37:28 AM
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1Gary
Posts: 256
Joined: 5/24/2008
Status: online
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Well if it is a vac leak,you could easily find it by just spraying it with carb cleaner.
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RE: Idle fluctuation - 8/26/2008 4:15:11 PM
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jkgray80
Posts: 118
Joined: 3/20/2008
Status: offline
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Just run your studs in & out a couple times & that will be good enough. As for ''no codes''. I hate that about people, i.e. "Well the dang ole light aint on & since the computer is smarter than me , aint nuthin wrong" You can have whats called a '' in perimeter'' failure. It will take someone that knows what they are lookng at when scanning through the computer. The info is there, they just arent seeing it. If you have emissions testing in your state, look for a state approved emissions repair shop.
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RE: Idle fluctuation - 9/4/2008 2:41:26 PM
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Scany
Posts: 40
Joined: 9/27/2007
Status: offline
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I haven''t done anything with the ground yet, but I did clean out the battery terminals that were kind of corroded, but not too bad. Guess I was eager to get it running and didn''t really think of it.
The problem is so funny because sometimes it''s fine and then all of the sudden it will start fluctuating.
I also have an issue that when I start from standstill it sounds like something mechanical is slipping and I hear a sounds like a small dog''s bark. Have yet to look into that, but could that be related maybe? I''m thinking if something in the driveline has slack to it and won''t stay stable. What leads me to think down the driveline is that the idle fluctuating is only when it''s in D, R, 3, 2, or 1. Not in N or P.
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