Deceleration, car bogs down...
Thread Starter
Advanced
Joined: Oct 2016
Posts: 76
Likes: 4
Deceleration, car bogs down...
1987 Coupe auto and a new issue just cropped up tonight.
When I decelerate, when taking my foot off the accelerator, the engine bogs down, and then comes back up again. No other noises or rattles, just the engine bogging down momentarily and then coming back.
When I decelerate, when taking my foot off the accelerator, the engine bogs down, and then comes back up again. No other noises or rattles, just the engine bogging down momentarily and then coming back.
Instructor
Joined: Dec 2016
Posts: 241
Likes: 77
From: Arlington VA
If it's an auto, that's engine braking. The torque converter clutch is engaged when you take your foot off the gas and disengages at 20-30 mph or so.
Thread Starter
Advanced
Joined: Oct 2016
Posts: 76
Likes: 4
Thanks for the info.
Le Mans Master
Joined: Aug 2015
Posts: 6,113
Likes: 1,994
From: St. Charles MO
Assuming you haven't changed any of the ECM calibrations, you should check your TPS and IAC. The ECM is programmed to use the IAC to give the engine a "soft" landing when the car is rolling and the throttle is returned to idle with the engine disengaged from the drivetrain. It uses the TPS to tell when the throttle has returned to zero, and the VSS to tell that the car is still rolling. The IAC is what actually manages the idle speed. I am assuming your speedometer is working fine because you didn't mention it, but if it isn't and the VSS is the cause then that will cause this kind of problem.
