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Vibration at idle in gear

N

NLRegina

New member
Joined
Dec 7, 2023
Hi everyone, wondering if this is normal behavior or indicative of an issue that can be resolved - 1991 740 with rex/regina, for the 10 months I've owned the vehicle, the idle is relatively smooth in neutral and park, but in drive or reverse (car is not moving), the idle drops from 750ish to about 600/500 and there is a noticeable amount of vibration being transferred through the car. I changed my engine mounts the day prior as part of my driveline vibration saga, wondering if the output flange angle is different than the pinion due to sagging mounts. The old ones were pushed in somewhat compared to new ones, but after changing them, the idle drops and the accompanying vibration have become slightly harsher. Any thoughts?
 
The idle air control is supposed to compensate for speed changes in idle due to a load change such as turning on the a/c or putting the trans in drive. I'd look around and make sure there aren't any vacuum leaks. Then move on to the idle system by checking the throttle position switch and idle air motor. Make sure you don't have a large vacuum leak from the PCV hoses being cracked and split.
 
dl242gt said:
The idle air control is supposed to compensate for speed changes in idle due to a load change such as turning on the a/c or putting the trans in drive. I'd look around and make sure there aren't any vacuum leaks. Then move on to the idle system by checking the throttle position switch and idle air motor. Make sure you don't have a large vacuum leak from the PCV hoses being cracked and split.
Click to expand...
I'll have to do a vacuum test for sure. I cleaned out my IAC valve again, nothing of note, applied 12v to open it, appears to be working fine. How would I determine a faulty IAC? What would I look for in a faulty TPS? I can hear a click sound on my initial turn of the throttle drum, throttle body is clean
 
NLRegina said:
I'll have to do a vacuum test for sure. I cleaned out my IAC valve again, nothing of note, applied 12v to open it, appears to be working fine. How would I determine a faulty IAC? What would I look for in a faulty TPS? I can hear a click sound on my initial turn of the throttle drum, throttle body is clean
Click to expand...
Test for a change in continuity at the plug. I've seen them click but not show any change before.
 
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