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1988 Buick Century, rough idle and stalls.

THEFERMANATOR

FRANKENBURBAN
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If it has the updated prom chip in it the MAF sensor is a waste of money. GM converted many of those from maf to speed density because the maf sensors were so problematic. Most left the maf inline as the intake air temp sensor in it was still used, but that was it.
 

WarWagon

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@THEFERMANATOR Do you recall how to tell if this SD update was done to this vehicle? This tidbit is almost lost to history. After the long shop times with the 1988 3.1L FWD Olds I would be stunned the shop would have missed that. (It was the new body Cutlass Supreme with the 3.1 V6. Could have been an late 1988 or 1989 I forget now.)

A little on the 2.8L was all I could find...


@MrMarty51

What engine is in this exactly? I was assuming it has the 3.8L V6. It could have the 2.8L looks like.

What does this have for an EGR valve on it? Possible it's sticking open (electric) or flapping full open if it's a vacuum and backpressure controlled unit. I have had the electric ones on other stuff stick full open stall me out when returning to idle or stopping.

Tap the ECM and see if the engine stalls. "Static Vibration Test" Aka "Thump It Twice" is looking for a loose connection in the device.
 

MrMarty51

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It has the wee 2.8.
Yup, vacuum opened EGR but I believe there is wires to the vacuum valve.
I’ll have to give the ECM the double tap and see what happens.
Just being layzeee today. Had some running to take care of, got that done and hadda sammich, feels like snoozing time now. 😵💫🤪😹
 

WarWagon

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If it still runs start it up, warm it up, drop in in drive. With the brakes on bring the engine up to 1200 RPM. This should kick the EGR vac solenoid on. If it starts running badly the EGR valve is flopping full open instead of moving via backpressure. (All electronic are just that without any vacuum to em.)
 

MrMarty51

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I’ll be sure to do that, between returning from Alaska and before it goes to the shop for the rest of the items thats getting replaced.
 

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FRANKENBURBAN
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The only way to tell if it is a speed density system is to check the PROM chip code and cross it to the TSB. I do know the ECM used on the 2.8l's were failure prone in the injector drivers. They use a batch fire injection system and over time the injector coils begin to short out creating extra current draw, and burns out the injector drivers. I fought one before, found the injector drivers were bad, replaced the ECM, but then had to do the injectors due to excess current draw. That was how I found out about the speed density update for them was I lucked out and found a PROM chip when I replaced the ECM.
 
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