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Username Post: slowed deceleration-to-idle speed        (Topic#356408)
Maynard G. Krebs 
Posts: 7

Reg: 02-21-19
05-13-19 03:19 PM - Post#2766315    

I have two 1989 Caprices, both the F41 sport suspension, both totally stock.. and otherwise operate just fine (and w/ good gas mileage).

Normal return-to-idle speed is severely hampered by some engine control. On a deserted road, if I am proceeding at most any speed, say 35 mph... if I suddenly take the car out of Drive and coast, it takes a good quarter-mile for the idle speed to return to normal. But before it does, the engine "races", similar to being on 'fast idle when cold'. This creates a borderline dangerous condition... in which the drivetrain (when engaged) fights any braking application... and handling is severely affected negatively. It's hard to drive... tiring & unpleasant. I'm supposed to enjoy driving them... but something is preventing that. Does anyone know??

I figure that it's either the emission-control system, perhaps the EGR system; OR, the fuel injection pump is significantly prevented from slowing down normally: it might be providing too much fuel-air mix upon decelerating, and/or engine controls are pumping excess air into the intake manifold, reducing the normal high intake vacuum Engine revs are too high.. for too long.. for good and safe handling. It is not simply a lack of 'engine braking' --- it is like the throttle mechanism having a strong hydraulic door-closing "dashpot" on it, which greatly slows the normal "return-to-idle" engine speed (revs).

My GM shop manual is of no help whatsoever.

Somebody must know how to fix this.

Edited by Maynard G. Krebs on 05-13-19 05:43 PM. Reason for edit: No reason given.


"8th Year" Gold Supporting Member
Posts: 3092
Age: 34
Loc: Utica ny
Reg: 04-13-10
12-31-19 09:49 AM - Post#2783313    
    In response to Maynard G. Krebs

2 things come to mind
sticking throttle at throttle body
or failing TPS (throttle position sensor)
Does it ever idle erratically?

Old School GM fan FOREVER


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