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Discussion Starter · #1 ·
Hello all, I am trying to fix a problem with my Impala/ Roadmaster and I was hoping that someone here has experienced the same issue. I have a complete stock 94 Buick Roadmaster with a 1977 Impala body...FYI

The problem I am having is when I drive for a short time, the engine begins to stumble and hesitate. I can hit the throttle, and it will hesitate for a moment, and then it will go. But when I let off the throttle, the car stumbles, and acts like it is running on four cylinders instead of eight. This happens after it has warmed up a tad. It will not die, it just acts as if it is about to, until I hit the throttle again. I have put a OBD1 scan tool on it and it is not showing any codes or malfunction other than a coolant sensor error. It also runs completely normally when in Park.

I have replaced the fuel filter, checked for proper fuel pressure, replaced the spark plugs with AC Delco Platinum Plugs, all with no results.

I am not sure if it could be an EGR valve problem, vacuum issue, or something much worse such as the Opti. Any help or recommendation would be greatly appreciated!
 

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It's probably the coolant sensor. If the coolant sensor that screws into the front of the waterpump is bad, and reading as though the car is still cold, it will cause the car to run extremely rich. I don't know that this would change in park vs. in gear, but other than that, it sounds to me like this is your most likely culprit.
 

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Discussion Starter · #3 · (Edited)
Update:

I have found what could be the problem. When i unhook the vacuum line from the EGR valve, the problem goes away. It comes right back when it is hooked up again.

Also i had a code stored in the PCM that was:

43 ESC Module or Sensor Circuit

It could have been knocking when the car was sputtering?


It wasn't the coolant sensor, according to the scanner (I misread it the first time).

Thanks Erik for that info!
 

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Sounds like you're right. Those are classic EGR symptoms. I would have suggested the EGR if it wasn't for the code you referred to. Really. No, really! LOL
 

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Discussion Starter · #5 ·
Thanks for the help. This one had me stumped! I am going to get a new valve put in and I will see how that works out.
 

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Discussion Starter · #6 ·
I disconnected the vaccuum line to the EGR valve, and now it is running nicely. I may go and get one that works, or leave it alone. It is hard to spend money on something that actually decreases performance!
 

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Makes sense. I don't think it's all that expensive or bad for performance though. There's an F-body egr that's a better replacement than the stock one. Somebody may have the part number handy. That's a hell of a project you undertook, by the way (I looked at your blog).
 

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Discussion Starter · #8 ·
Thanks for checking out the blog. It has taken me alot of time, and a little bit of money, but it sure has been fun. I will look for that F-Body EGR. Thanks for the info!
 

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i checked out the blog to that box chevy loves you for restoring it!!!:biggrin:
 
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