Idle speed on my 1987 Mercury Grand Marquis is going up and down - what' s wrong ?
Asked by froeschl Dec 18, 2016 at 05:26 AM about the 1987 Mercury Grand Marquis
Question type: Maintenance & Repair
When my Mercury is running for a while at idle speed, engine speed suddenly starts going up and down. Sometimes the engine even turns off after a few seconds. I checked all vacuum hoses - they seem to be OK. Can it be any sensor or valve causing this problem ? While driving everything is OK. This only occurs when enging is idling and the selector lever is set to "P".
5 Answers
Sounds as if the air idle control is defective or needs to be cleaned..
http://www.partsgeek.com/catalog/1987/merc ury/grand_marquis/fuel_injection/idle_control_v alve.html
Trippmeister answered 8 years ago
Could it also be the TPS? (Throttle position sensor). They do wear out sometimes.
clean the throttle plate of carbon, relearn idle by putting front of car against wall or pole warmed up, disconnect neg batt cable for 20 min, reconnect cable, start up & run at idle for 2 min in park w/ accessories off, then put in drive for 2 min brake off, that should do it.
My 86 did that. How does the car relearn idle. When you put the front against a wall does it need to be in drive lol? I need help with mine I think my throttle position sensor is bad it started accelerating on it’s own and when in park sounded like it was floored. I revved it and let off fast and it idled down for legit a second then it when right back up. I drove it home the way I hate to say luckily getting all green lights almost. Half way back it started acting normal off and on. It idled normal a couple time when I did I have to stop but right before light turned green it idled way back up again then the engine would miss out real bad then it’d act “normal”temporarily
