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When in gear (ex. Reverse, Drive, 2nd, 1st) my car idle "settles" around 750 on the tach, but then starts to fluctuate around there, moving up to 900(or so) then dips down to about 500 on the tach. While the idle speed is fluctuating my voltage drops dramatically. It will go from about 14 on the volt meter down to about 9, but not in the red - 8 on the volt meter. I recently replaced all the plugs, fuel filter and a casket on the #8 exhaust port, new oil filter, and a voltage burn-off relay. I am torn between whether it is the Mass Air Flow sensor, the Throttle Position Sensor or the Oxygen sensor. If anyone has ANY information about this type of a problem please contact me.
 

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My 88 Iroc-z 350 did the exact same thing. It does it every now and then. Every once in a while it would get so bad that it stalled, throwing the check engine light on. I took it to the garage, and they said that they got a mass air flow trouble code, but they couldn't find the exact problem. They said the mass air flow could have problems, but they didn't recommend replacing it due to the price. They told me to continue driving it till it got to be a continuing problem. That was a year ago, and it still runs fine. Has idle problem about one day a week.
 

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Cyris,
Take a real good look at the throttle "butterfly" valve. They have a tendency to get buildup with dirt and will stick slightly open, confusing the computer into thinking that you are pushing on the "go" pedal. Get some carb cleaner, or even better, GM Top Engine cleaner, and really clean out the throttle valve and air intake area. I have seen several similar problems fixed this way. If this does not take care of it, it may be worth paying someone an hours labor to hook up a good scanner and see what is going on. You can waste a lot of money on the newer cars throwing a lot of expensive parts at them and still not fixing the problem. It could be a simple loose connection somewhere. A good tech can catch this type of stuff with a good scan tool.
Hope this helps,

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md
 

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BillK- Good advice as usual! Also, you might check the ground wires that are located at various places on the engine...at the t-stat housing, on the left bank of the exhaust manifold area, rear of the engine at trans...etc. a bad ground will run havoc!!
 

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Always check the fuel pressure on these guys.
It might be the in tank fuel pump or clogged filter. I had a similar problem on my 88 T/A some years back. No one bothered to check the fuel pressure, I assumed they did (bad word). I checked and it was low.
 

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I have an 88 irocz that had the same problem. Try unhooking your mass air sensor for a minute. your check engine light will come on but don't worry about that. See if it runs any better like that. if it does then your mass air sensor is bad, If not check your throtle posistion sensor and make sure it is positioned right
 

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I'm going to say check your IAC valve (idle air control), this is located on the passenger side underneath the throttle body. These get all carboned up and can't re-seat themselves properly. You may have to perform a minimum idle setting also. This isn't to hard but is more complicated than on a non-computer controlled car.

Bill makes a good point about testing certain components before shotgunning parts into it. There are a few field tests you can do yourself with just a digital ohm meter and common hand tools.

Good Luck!


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67 Camaro LS6 454/TH400/12bolt 3.73
1989 TransAm 5.7L WS6 W/all the options
 

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I am going to say to check the timing to see if it is right. If the timing is off a little it might idle in park but not when it is gear like drive. My 88 iroc wouldn't idle in gear but it would idle in park so I checked the timing and it was off a little and it helped my idleing a lot when the car is in gear. I hope this helps some one.

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michael gunnells
 

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If you have idle and just off idle problems, check the EGR valve by pulling the vac line off it.
You will get some pinging due to no EGR flow, but if the idle or just off idle improves, the EGR is opening too fast due to carbon buildup inside the valve and must be replaced.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer
 

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i have an 88 iroc with a lb9 and im having the same trouble somedays it will run fine but other the rpms will drop and raise and die if not given gas the timing is e dead on and ive even bumped idle screw up to 2k in neural just to see what it does and it prevents it from dieing but still drops 500 and when in gear runs longer but still dies im out of ideas but to start changing all senors anyone got better idea?
 

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First thing to do is to clean around and behind the throttle blades, those TPI engines collect egr soot right behind the blades.
David
 

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did u ever get problem fixed? If not check ur fuel injectors because my 87 roc was doing the same thing as urs and i tried everything and come to find out my fuel injectors wre causing the whole problem.
 
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