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94 DEVILLE Serivice Engine Soon Light ??


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Hello Again,

You guys were so nice to help me out last time I was here thought I'd call on your expertise once again. I drove my 94 deville 4.9 just 3 miles to the post office today.. the Service Engine Soon light came on... when I came out of the post office and started up it was off and did not come back on, I drove home. I have started the car since but not driven it and it has not come back on. I read some older posts to see if they could help me figure it out and went out to check the codes.. this is what I got ...

P030 History

No IPC Code

C ode A040 History

No SIR Code

No TCS Code


I didn't see anything that said CURRENT. Do you think I have a problem? I'd rather deal with it early on than cause any kind of damage. The vehicle doen't seem to have any problems...??? Seemed to run normal. Thanks so much Cassie

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P030 (E030) ................................................... ISC RPM out of range

A040 .......................................... Air Mix Valve (Door) Circuit Problem

P030 is Idle Speed Control Motor. May need adjustment or replacement. Won't cause any damage. Poor idle is worst case.

A040 is heater related. Worst case is your not getting the temp requested.

Since the codes are history, I'd clear 'em and see if they return. run the codes again in a week if no SES light comes on.

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If the ISC motor original it may need replacement. Does it make unusually loud ratcheting noise when you shut down th engine? As Ranger noticed, there's nothing to worry so far.

The saddest thing in life is wasted talent

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I had the same problem with my 1994 Deville and it turned out that there was just a very low oil pressure level and once I got a new oil change, the light was gone and I have not seen it since. Just hope that the oil pressure level is not low due to an oil leak.

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