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Before I get real serious regarding repeatable subject codes 90 and 91 - "fuel Control, Cyl #1-4, and Cyl #5-8", I thought I would ask if any of you have had the codes and a verified root cause and fix. I have a theory which may be out-of-line.

The SES lights almost exclusively after the car is warm, and the engine is allowed to return to idle after depressing the clutch to drift to a brake assisted stop. I notice a short period of lumpy idle then immediately SES, immediate stop, check codes, only 90 and 91, both codes always present. The MAFs are bran-new - thanks to DavidS $115 GB (David, you forgot to send me the screws!).

My hypothesis is a vacuum leak in the brake boost line. The theory is that with the engine at speed, it has an excess of vacuum and therefore no problem for most stops. But, allow the engine to settle at idle for a bit (during coasting), then go for the brakes - leak causes vacuum deficit, deficit impacts idle, ... Granted, I cannot answer the intermittent nature of this failure given that many braking intervals at or near idle are supported without the lumpy idle, SES, and codes.

Any better ideas before I get serious?

Thanks in advance

Mike
 

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This is kind of an old thread and Michael hasn't logged on since last October so he may not answer you. Good luck with your codes.
 
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